1 /* 2 * linux/fs/namei.c 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 */ 6 7 /* 8 * Some corrections by tytso. 9 */ 10 11 /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname 12 * lookup logic. 13 */ 14 /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture. 15 */ 16 17 #include <linux/init.h> 18 #include <linux/export.h> 19 #include <linux/kernel.h> 20 #include <linux/slab.h> 21 #include <linux/fs.h> 22 #include <linux/namei.h> 23 #include <linux/pagemap.h> 24 #include <linux/fsnotify.h> 25 #include <linux/personality.h> 26 #include <linux/security.h> 27 #include <linux/ima.h> 28 #include <linux/syscalls.h> 29 #include <linux/mount.h> 30 #include <linux/audit.h> 31 #include <linux/capability.h> 32 #include <linux/file.h> 33 #include <linux/fcntl.h> 34 #include <linux/device_cgroup.h> 35 #include <linux/fs_struct.h> 36 #include <linux/posix_acl.h> 37 #include <asm/uaccess.h> 38 39 #include "internal.h" 40 #include "mount.h" 41 42 /* [Feb-1997 T. Schoebel-Theuer] 43 * Fundamental changes in the pathname lookup mechanisms (namei) 44 * were necessary because of omirr. The reason is that omirr needs 45 * to know the _real_ pathname, not the user-supplied one, in case 46 * of symlinks (and also when transname replacements occur). 47 * 48 * The new code replaces the old recursive symlink resolution with 49 * an iterative one (in case of non-nested symlink chains). It does 50 * this with calls to <fs>_follow_link(). 51 * As a side effect, dir_namei(), _namei() and follow_link() are now 52 * replaced with a single function lookup_dentry() that can handle all 53 * the special cases of the former code. 54 * 55 * With the new dcache, the pathname is stored at each inode, at least as 56 * long as the refcount of the inode is positive. As a side effect, the 57 * size of the dcache depends on the inode cache and thus is dynamic. 58 * 59 * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink 60 * resolution to correspond with current state of the code. 61 * 62 * Note that the symlink resolution is not *completely* iterative. 63 * There is still a significant amount of tail- and mid- recursion in 64 * the algorithm. Also, note that <fs>_readlink() is not used in 65 * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink() 66 * may return different results than <fs>_follow_link(). Many virtual 67 * filesystems (including /proc) exhibit this behavior. 68 */ 69 70 /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation: 71 * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL 72 * and the name already exists in form of a symlink, try to create the new 73 * name indicated by the symlink. The old code always complained that the 74 * name already exists, due to not following the symlink even if its target 75 * is nonexistent. The new semantics affects also mknod() and link() when 76 * the name is a symlink pointing to a non-existent name. 77 * 78 * I don't know which semantics is the right one, since I have no access 79 * to standards. But I found by trial that HP-UX 9.0 has the full "new" 80 * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the 81 * "old" one. Personally, I think the new semantics is much more logical. 82 * Note that "ln old new" where "new" is a symlink pointing to a non-existing 83 * file does succeed in both HP-UX and SunOs, but not in Solaris 84 * and in the old Linux semantics. 85 */ 86 87 /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink 88 * semantics. See the comments in "open_namei" and "do_link" below. 89 * 90 * [10-Sep-98 Alan Modra] Another symlink change. 91 */ 92 93 /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks: 94 * inside the path - always follow. 95 * in the last component in creation/removal/renaming - never follow. 96 * if LOOKUP_FOLLOW passed - follow. 97 * if the pathname has trailing slashes - follow. 98 * otherwise - don't follow. 99 * (applied in that order). 100 * 101 * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT 102 * restored for 2.4. This is the last surviving part of old 4.2BSD bug. 103 * During the 2.4 we need to fix the userland stuff depending on it - 104 * hopefully we will be able to get rid of that wart in 2.5. So far only 105 * XEmacs seems to be relying on it... 106 */ 107 /* 108 * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland) 109 * implemented. Let's see if raised priority of ->s_vfs_rename_mutex gives 110 * any extra contention... 111 */ 112 113 /* In order to reduce some races, while at the same time doing additional 114 * checking and hopefully speeding things up, we copy filenames to the 115 * kernel data space before using them.. 116 * 117 * POSIX.1 2.4: an empty pathname is invalid (ENOENT). 118 * PATH_MAX includes the nul terminator --RR. 119 */ 120 void final_putname(struct filename *name) 121 { 122 if (name->separate) { 123 __putname(name->name); 124 kfree(name); 125 } else { 126 __putname(name); 127 } 128 } 129 130 #define EMBEDDED_NAME_MAX (PATH_MAX - sizeof(struct filename)) 131 132 static struct filename * 133 getname_flags(const char __user *filename, int flags, int *empty) 134 { 135 struct filename *result, *err; 136 int len; 137 long max; 138 char *kname; 139 140 result = audit_reusename(filename); 141 if (result) 142 return result; 143 144 result = __getname(); 145 if (unlikely(!result)) 146 return ERR_PTR(-ENOMEM); 147 148 /* 149 * First, try to embed the struct filename inside the names_cache 150 * allocation 151 */ 152 kname = (char *)result + sizeof(*result); 153 result->name = kname; 154 result->separate = false; 155 max = EMBEDDED_NAME_MAX; 156 157 recopy: 158 len = strncpy_from_user(kname, filename, max); 159 if (unlikely(len < 0)) { 160 err = ERR_PTR(len); 161 goto error; 162 } 163 164 /* 165 * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a 166 * separate struct filename so we can dedicate the entire 167 * names_cache allocation for the pathname, and re-do the copy from 168 * userland. 169 */ 170 if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) { 171 kname = (char *)result; 172 173 result = kzalloc(sizeof(*result), GFP_KERNEL); 174 if (!result) { 175 err = ERR_PTR(-ENOMEM); 176 result = (struct filename *)kname; 177 goto error; 178 } 179 result->name = kname; 180 result->separate = true; 181 max = PATH_MAX; 182 goto recopy; 183 } 184 185 /* The empty path is special. */ 186 if (unlikely(!len)) { 187 if (empty) 188 *empty = 1; 189 err = ERR_PTR(-ENOENT); 190 if (!(flags & LOOKUP_EMPTY)) 191 goto error; 192 } 193 194 err = ERR_PTR(-ENAMETOOLONG); 195 if (unlikely(len >= PATH_MAX)) 196 goto error; 197 198 result->uptr = filename; 199 audit_getname(result); 200 return result; 201 202 error: 203 final_putname(result); 204 return err; 205 } 206 207 struct filename * 208 getname(const char __user * filename) 209 { 210 return getname_flags(filename, 0, NULL); 211 } 212 EXPORT_SYMBOL(getname); 213 214 #ifdef CONFIG_AUDITSYSCALL 215 void putname(struct filename *name) 216 { 217 if (unlikely(!audit_dummy_context())) 218 return audit_putname(name); 219 final_putname(name); 220 } 221 #endif 222 223 static int check_acl(struct inode *inode, int mask) 224 { 225 #ifdef CONFIG_FS_POSIX_ACL 226 struct posix_acl *acl; 227 228 if (mask & MAY_NOT_BLOCK) { 229 acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS); 230 if (!acl) 231 return -EAGAIN; 232 /* no ->get_acl() calls in RCU mode... */ 233 if (acl == ACL_NOT_CACHED) 234 return -ECHILD; 235 return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK); 236 } 237 238 acl = get_cached_acl(inode, ACL_TYPE_ACCESS); 239 240 /* 241 * A filesystem can force a ACL callback by just never filling the 242 * ACL cache. But normally you'd fill the cache either at inode 243 * instantiation time, or on the first ->get_acl call. 244 * 245 * If the filesystem doesn't have a get_acl() function at all, we'll 246 * just create the negative cache entry. 247 */ 248 if (acl == ACL_NOT_CACHED) { 249 if (inode->i_op->get_acl) { 250 acl = inode->i_op->get_acl(inode, ACL_TYPE_ACCESS); 251 if (IS_ERR(acl)) 252 return PTR_ERR(acl); 253 } else { 254 set_cached_acl(inode, ACL_TYPE_ACCESS, NULL); 255 return -EAGAIN; 256 } 257 } 258 259 if (acl) { 260 int error = posix_acl_permission(inode, acl, mask); 261 posix_acl_release(acl); 262 return error; 263 } 264 #endif 265 266 return -EAGAIN; 267 } 268 269 /* 270 * This does the basic permission checking 271 */ 272 static int acl_permission_check(struct inode *inode, int mask) 273 { 274 unsigned int mode = inode->i_mode; 275 276 if (likely(uid_eq(current_fsuid(), inode->i_uid))) 277 mode >>= 6; 278 else { 279 if (IS_POSIXACL(inode) && (mode & S_IRWXG)) { 280 int error = check_acl(inode, mask); 281 if (error != -EAGAIN) 282 return error; 283 } 284 285 if (in_group_p(inode->i_gid)) 286 mode >>= 3; 287 } 288 289 /* 290 * If the DACs are ok we don't need any capability check. 291 */ 292 if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0) 293 return 0; 294 return -EACCES; 295 } 296 297 /** 298 * generic_permission - check for access rights on a Posix-like filesystem 299 * @inode: inode to check access rights for 300 * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...) 301 * 302 * Used to check for read/write/execute permissions on a file. 303 * We use "fsuid" for this, letting us set arbitrary permissions 304 * for filesystem access without changing the "normal" uids which 305 * are used for other things. 306 * 307 * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk 308 * request cannot be satisfied (eg. requires blocking or too much complexity). 309 * It would then be called again in ref-walk mode. 310 */ 311 int generic_permission(struct inode *inode, int mask) 312 { 313 int ret; 314 315 /* 316 * Do the basic permission checks. 317 */ 318 ret = acl_permission_check(inode, mask); 319 if (ret != -EACCES) 320 return ret; 321 322 if (S_ISDIR(inode->i_mode)) { 323 /* DACs are overridable for directories */ 324 if (inode_capable(inode, CAP_DAC_OVERRIDE)) 325 return 0; 326 if (!(mask & MAY_WRITE)) 327 if (inode_capable(inode, CAP_DAC_READ_SEARCH)) 328 return 0; 329 return -EACCES; 330 } 331 /* 332 * Read/write DACs are always overridable. 333 * Executable DACs are overridable when there is 334 * at least one exec bit set. 335 */ 336 if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO)) 337 if (inode_capable(inode, CAP_DAC_OVERRIDE)) 338 return 0; 339 340 /* 341 * Searching includes executable on directories, else just read. 342 */ 343 mask &= MAY_READ | MAY_WRITE | MAY_EXEC; 344 if (mask == MAY_READ) 345 if (inode_capable(inode, CAP_DAC_READ_SEARCH)) 346 return 0; 347 348 return -EACCES; 349 } 350 351 /* 352 * We _really_ want to just do "generic_permission()" without 353 * even looking at the inode->i_op values. So we keep a cache 354 * flag in inode->i_opflags, that says "this has not special 355 * permission function, use the fast case". 356 */ 357 static inline int do_inode_permission(struct inode *inode, int mask) 358 { 359 if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) { 360 if (likely(inode->i_op->permission)) 361 return inode->i_op->permission(inode, mask); 362 363 /* This gets set once for the inode lifetime */ 364 spin_lock(&inode->i_lock); 365 inode->i_opflags |= IOP_FASTPERM; 366 spin_unlock(&inode->i_lock); 367 } 368 return generic_permission(inode, mask); 369 } 370 371 /** 372 * __inode_permission - Check for access rights to a given inode 373 * @inode: Inode to check permission on 374 * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) 375 * 376 * Check for read/write/execute permissions on an inode. 377 * 378 * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask. 379 * 380 * This does not check for a read-only file system. You probably want 381 * inode_permission(). 382 */ 383 int __inode_permission(struct inode *inode, int mask) 384 { 385 int retval; 386 387 if (unlikely(mask & MAY_WRITE)) { 388 /* 389 * Nobody gets write access to an immutable file. 390 */ 391 if (IS_IMMUTABLE(inode)) 392 return -EACCES; 393 } 394 395 retval = do_inode_permission(inode, mask); 396 if (retval) 397 return retval; 398 399 retval = devcgroup_inode_permission(inode, mask); 400 if (retval) 401 return retval; 402 403 return security_inode_permission(inode, mask); 404 } 405 406 /** 407 * sb_permission - Check superblock-level permissions 408 * @sb: Superblock of inode to check permission on 409 * @inode: Inode to check permission on 410 * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) 411 * 412 * Separate out file-system wide checks from inode-specific permission checks. 413 */ 414 static int sb_permission(struct super_block *sb, struct inode *inode, int mask) 415 { 416 if (unlikely(mask & MAY_WRITE)) { 417 umode_t mode = inode->i_mode; 418 419 /* Nobody gets write access to a read-only fs. */ 420 if ((sb->s_flags & MS_RDONLY) && 421 (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) 422 return -EROFS; 423 } 424 return 0; 425 } 426 427 /** 428 * inode_permission - Check for access rights to a given inode 429 * @inode: Inode to check permission on 430 * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) 431 * 432 * Check for read/write/execute permissions on an inode. We use fs[ug]id for 433 * this, letting us set arbitrary permissions for filesystem access without 434 * changing the "normal" UIDs which are used for other things. 435 * 436 * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask. 437 */ 438 int inode_permission(struct inode *inode, int mask) 439 { 440 int retval; 441 442 retval = sb_permission(inode->i_sb, inode, mask); 443 if (retval) 444 return retval; 445 return __inode_permission(inode, mask); 446 } 447 448 /** 449 * path_get - get a reference to a path 450 * @path: path to get the reference to 451 * 452 * Given a path increment the reference count to the dentry and the vfsmount. 453 */ 454 void path_get(struct path *path) 455 { 456 mntget(path->mnt); 457 dget(path->dentry); 458 } 459 EXPORT_SYMBOL(path_get); 460 461 /** 462 * path_put - put a reference to a path 463 * @path: path to put the reference to 464 * 465 * Given a path decrement the reference count to the dentry and the vfsmount. 466 */ 467 void path_put(struct path *path) 468 { 469 dput(path->dentry); 470 mntput(path->mnt); 471 } 472 EXPORT_SYMBOL(path_put); 473 474 /* 475 * Path walking has 2 modes, rcu-walk and ref-walk (see 476 * Documentation/filesystems/path-lookup.txt). In situations when we can't 477 * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab 478 * normal reference counts on dentries and vfsmounts to transition to rcu-walk 479 * mode. Refcounts are grabbed at the last known good point before rcu-walk 480 * got stuck, so ref-walk may continue from there. If this is not successful 481 * (eg. a seqcount has changed), then failure is returned and it's up to caller 482 * to restart the path walk from the beginning in ref-walk mode. 483 */ 484 485 static inline void lock_rcu_walk(void) 486 { 487 br_read_lock(&vfsmount_lock); 488 rcu_read_lock(); 489 } 490 491 static inline void unlock_rcu_walk(void) 492 { 493 rcu_read_unlock(); 494 br_read_unlock(&vfsmount_lock); 495 } 496 497 /** 498 * unlazy_walk - try to switch to ref-walk mode. 499 * @nd: nameidata pathwalk data 500 * @dentry: child of nd->path.dentry or NULL 501 * Returns: 0 on success, -ECHILD on failure 502 * 503 * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry 504 * for ref-walk mode. @dentry must be a path found by a do_lookup call on 505 * @nd or NULL. Must be called from rcu-walk context. 506 */ 507 static int unlazy_walk(struct nameidata *nd, struct dentry *dentry) 508 { 509 struct fs_struct *fs = current->fs; 510 struct dentry *parent = nd->path.dentry; 511 int want_root = 0; 512 513 BUG_ON(!(nd->flags & LOOKUP_RCU)); 514 if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { 515 want_root = 1; 516 spin_lock(&fs->lock); 517 if (nd->root.mnt != fs->root.mnt || 518 nd->root.dentry != fs->root.dentry) 519 goto err_root; 520 } 521 spin_lock(&parent->d_lock); 522 if (!dentry) { 523 if (!__d_rcu_to_refcount(parent, nd->seq)) 524 goto err_parent; 525 BUG_ON(nd->inode != parent->d_inode); 526 } else { 527 if (dentry->d_parent != parent) 528 goto err_parent; 529 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); 530 if (!__d_rcu_to_refcount(dentry, nd->seq)) 531 goto err_child; 532 /* 533 * If the sequence check on the child dentry passed, then 534 * the child has not been removed from its parent. This 535 * means the parent dentry must be valid and able to take 536 * a reference at this point. 537 */ 538 BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent); 539 BUG_ON(!parent->d_count); 540 parent->d_count++; 541 spin_unlock(&dentry->d_lock); 542 } 543 spin_unlock(&parent->d_lock); 544 if (want_root) { 545 path_get(&nd->root); 546 spin_unlock(&fs->lock); 547 } 548 mntget(nd->path.mnt); 549 550 unlock_rcu_walk(); 551 nd->flags &= ~LOOKUP_RCU; 552 return 0; 553 554 err_child: 555 spin_unlock(&dentry->d_lock); 556 err_parent: 557 spin_unlock(&parent->d_lock); 558 err_root: 559 if (want_root) 560 spin_unlock(&fs->lock); 561 return -ECHILD; 562 } 563 564 static inline int d_revalidate(struct dentry *dentry, unsigned int flags) 565 { 566 return dentry->d_op->d_revalidate(dentry, flags); 567 } 568 569 /** 570 * complete_walk - successful completion of path walk 571 * @nd: pointer nameidata 572 * 573 * If we had been in RCU mode, drop out of it and legitimize nd->path. 574 * Revalidate the final result, unless we'd already done that during 575 * the path walk or the filesystem doesn't ask for it. Return 0 on 576 * success, -error on failure. In case of failure caller does not 577 * need to drop nd->path. 578 */ 579 static int complete_walk(struct nameidata *nd) 580 { 581 struct dentry *dentry = nd->path.dentry; 582 int status; 583 584 if (nd->flags & LOOKUP_RCU) { 585 nd->flags &= ~LOOKUP_RCU; 586 if (!(nd->flags & LOOKUP_ROOT)) 587 nd->root.mnt = NULL; 588 spin_lock(&dentry->d_lock); 589 if (unlikely(!__d_rcu_to_refcount(dentry, nd->seq))) { 590 spin_unlock(&dentry->d_lock); 591 unlock_rcu_walk(); 592 return -ECHILD; 593 } 594 BUG_ON(nd->inode != dentry->d_inode); 595 spin_unlock(&dentry->d_lock); 596 mntget(nd->path.mnt); 597 unlock_rcu_walk(); 598 } 599 600 if (likely(!(nd->flags & LOOKUP_JUMPED))) 601 return 0; 602 603 if (likely(!(dentry->d_flags & DCACHE_OP_REVALIDATE))) 604 return 0; 605 606 if (likely(!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT))) 607 return 0; 608 609 /* Note: we do not d_invalidate() */ 610 status = d_revalidate(dentry, nd->flags); 611 if (status > 0) 612 return 0; 613 614 if (!status) 615 status = -ESTALE; 616 617 path_put(&nd->path); 618 return status; 619 } 620 621 static __always_inline void set_root(struct nameidata *nd) 622 { 623 if (!nd->root.mnt) 624 get_fs_root(current->fs, &nd->root); 625 } 626 627 static int link_path_walk(const char *, struct nameidata *); 628 629 static __always_inline void set_root_rcu(struct nameidata *nd) 630 { 631 if (!nd->root.mnt) { 632 struct fs_struct *fs = current->fs; 633 unsigned seq; 634 635 do { 636 seq = read_seqcount_begin(&fs->seq); 637 nd->root = fs->root; 638 nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq); 639 } while (read_seqcount_retry(&fs->seq, seq)); 640 } 641 } 642 643 static __always_inline int __vfs_follow_link(struct nameidata *nd, const char *link) 644 { 645 int ret; 646 647 if (IS_ERR(link)) 648 goto fail; 649 650 if (*link == '/') { 651 set_root(nd); 652 path_put(&nd->path); 653 nd->path = nd->root; 654 path_get(&nd->root); 655 nd->flags |= LOOKUP_JUMPED; 656 } 657 nd->inode = nd->path.dentry->d_inode; 658 659 ret = link_path_walk(link, nd); 660 return ret; 661 fail: 662 path_put(&nd->path); 663 return PTR_ERR(link); 664 } 665 666 static void path_put_conditional(struct path *path, struct nameidata *nd) 667 { 668 dput(path->dentry); 669 if (path->mnt != nd->path.mnt) 670 mntput(path->mnt); 671 } 672 673 static inline void path_to_nameidata(const struct path *path, 674 struct nameidata *nd) 675 { 676 if (!(nd->flags & LOOKUP_RCU)) { 677 dput(nd->path.dentry); 678 if (nd->path.mnt != path->mnt) 679 mntput(nd->path.mnt); 680 } 681 nd->path.mnt = path->mnt; 682 nd->path.dentry = path->dentry; 683 } 684 685 /* 686 * Helper to directly jump to a known parsed path from ->follow_link, 687 * caller must have taken a reference to path beforehand. 688 */ 689 void nd_jump_link(struct nameidata *nd, struct path *path) 690 { 691 path_put(&nd->path); 692 693 nd->path = *path; 694 nd->inode = nd->path.dentry->d_inode; 695 nd->flags |= LOOKUP_JUMPED; 696 697 BUG_ON(nd->inode->i_op->follow_link); 698 } 699 700 static inline void put_link(struct nameidata *nd, struct path *link, void *cookie) 701 { 702 struct inode *inode = link->dentry->d_inode; 703 if (inode->i_op->put_link) 704 inode->i_op->put_link(link->dentry, nd, cookie); 705 path_put(link); 706 } 707 708 int sysctl_protected_symlinks __read_mostly = 0; 709 int sysctl_protected_hardlinks __read_mostly = 0; 710 711 /** 712 * may_follow_link - Check symlink following for unsafe situations 713 * @link: The path of the symlink 714 * @nd: nameidata pathwalk data 715 * 716 * In the case of the sysctl_protected_symlinks sysctl being enabled, 717 * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is 718 * in a sticky world-writable directory. This is to protect privileged 719 * processes from failing races against path names that may change out 720 * from under them by way of other users creating malicious symlinks. 721 * It will permit symlinks to be followed only when outside a sticky 722 * world-writable directory, or when the uid of the symlink and follower 723 * match, or when the directory owner matches the symlink's owner. 724 * 725 * Returns 0 if following the symlink is allowed, -ve on error. 726 */ 727 static inline int may_follow_link(struct path *link, struct nameidata *nd) 728 { 729 const struct inode *inode; 730 const struct inode *parent; 731 732 if (!sysctl_protected_symlinks) 733 return 0; 734 735 /* Allowed if owner and follower match. */ 736 inode = link->dentry->d_inode; 737 if (uid_eq(current_cred()->fsuid, inode->i_uid)) 738 return 0; 739 740 /* Allowed if parent directory not sticky and world-writable. */ 741 parent = nd->path.dentry->d_inode; 742 if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH)) 743 return 0; 744 745 /* Allowed if parent directory and link owner match. */ 746 if (uid_eq(parent->i_uid, inode->i_uid)) 747 return 0; 748 749 audit_log_link_denied("follow_link", link); 750 path_put_conditional(link, nd); 751 path_put(&nd->path); 752 return -EACCES; 753 } 754 755 /** 756 * safe_hardlink_source - Check for safe hardlink conditions 757 * @inode: the source inode to hardlink from 758 * 759 * Return false if at least one of the following conditions: 760 * - inode is not a regular file 761 * - inode is setuid 762 * - inode is setgid and group-exec 763 * - access failure for read and write 764 * 765 * Otherwise returns true. 766 */ 767 static bool safe_hardlink_source(struct inode *inode) 768 { 769 umode_t mode = inode->i_mode; 770 771 /* Special files should not get pinned to the filesystem. */ 772 if (!S_ISREG(mode)) 773 return false; 774 775 /* Setuid files should not get pinned to the filesystem. */ 776 if (mode & S_ISUID) 777 return false; 778 779 /* Executable setgid files should not get pinned to the filesystem. */ 780 if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) 781 return false; 782 783 /* Hardlinking to unreadable or unwritable sources is dangerous. */ 784 if (inode_permission(inode, MAY_READ | MAY_WRITE)) 785 return false; 786 787 return true; 788 } 789 790 /** 791 * may_linkat - Check permissions for creating a hardlink 792 * @link: the source to hardlink from 793 * 794 * Block hardlink when all of: 795 * - sysctl_protected_hardlinks enabled 796 * - fsuid does not match inode 797 * - hardlink source is unsafe (see safe_hardlink_source() above) 798 * - not CAP_FOWNER 799 * 800 * Returns 0 if successful, -ve on error. 801 */ 802 static int may_linkat(struct path *link) 803 { 804 const struct cred *cred; 805 struct inode *inode; 806 807 if (!sysctl_protected_hardlinks) 808 return 0; 809 810 cred = current_cred(); 811 inode = link->dentry->d_inode; 812 813 /* Source inode owner (or CAP_FOWNER) can hardlink all they like, 814 * otherwise, it must be a safe source. 815 */ 816 if (uid_eq(cred->fsuid, inode->i_uid) || safe_hardlink_source(inode) || 817 capable(CAP_FOWNER)) 818 return 0; 819 820 audit_log_link_denied("linkat", link); 821 return -EPERM; 822 } 823 824 static __always_inline int 825 follow_link(struct path *link, struct nameidata *nd, void **p) 826 { 827 struct dentry *dentry = link->dentry; 828 int error; 829 char *s; 830 831 BUG_ON(nd->flags & LOOKUP_RCU); 832 833 if (link->mnt == nd->path.mnt) 834 mntget(link->mnt); 835 836 error = -ELOOP; 837 if (unlikely(current->total_link_count >= 40)) 838 goto out_put_nd_path; 839 840 cond_resched(); 841 current->total_link_count++; 842 843 touch_atime(link); 844 nd_set_link(nd, NULL); 845 846 error = security_inode_follow_link(link->dentry, nd); 847 if (error) 848 goto out_put_nd_path; 849 850 nd->last_type = LAST_BIND; 851 *p = dentry->d_inode->i_op->follow_link(dentry, nd); 852 error = PTR_ERR(*p); 853 if (IS_ERR(*p)) 854 goto out_put_nd_path; 855 856 error = 0; 857 s = nd_get_link(nd); 858 if (s) { 859 error = __vfs_follow_link(nd, s); 860 if (unlikely(error)) 861 put_link(nd, link, *p); 862 } 863 864 return error; 865 866 out_put_nd_path: 867 *p = NULL; 868 path_put(&nd->path); 869 path_put(link); 870 return error; 871 } 872 873 static int follow_up_rcu(struct path *path) 874 { 875 struct mount *mnt = real_mount(path->mnt); 876 struct mount *parent; 877 struct dentry *mountpoint; 878 879 parent = mnt->mnt_parent; 880 if (&parent->mnt == path->mnt) 881 return 0; 882 mountpoint = mnt->mnt_mountpoint; 883 path->dentry = mountpoint; 884 path->mnt = &parent->mnt; 885 return 1; 886 } 887 888 /* 889 * follow_up - Find the mountpoint of path's vfsmount 890 * 891 * Given a path, find the mountpoint of its source file system. 892 * Replace @path with the path of the mountpoint in the parent mount. 893 * Up is towards /. 894 * 895 * Return 1 if we went up a level and 0 if we were already at the 896 * root. 897 */ 898 int follow_up(struct path *path) 899 { 900 struct mount *mnt = real_mount(path->mnt); 901 struct mount *parent; 902 struct dentry *mountpoint; 903 904 br_read_lock(&vfsmount_lock); 905 parent = mnt->mnt_parent; 906 if (parent == mnt) { 907 br_read_unlock(&vfsmount_lock); 908 return 0; 909 } 910 mntget(&parent->mnt); 911 mountpoint = dget(mnt->mnt_mountpoint); 912 br_read_unlock(&vfsmount_lock); 913 dput(path->dentry); 914 path->dentry = mountpoint; 915 mntput(path->mnt); 916 path->mnt = &parent->mnt; 917 return 1; 918 } 919 920 /* 921 * Perform an automount 922 * - return -EISDIR to tell follow_managed() to stop and return the path we 923 * were called with. 924 */ 925 static int follow_automount(struct path *path, unsigned flags, 926 bool *need_mntput) 927 { 928 struct vfsmount *mnt; 929 int err; 930 931 if (!path->dentry->d_op || !path->dentry->d_op->d_automount) 932 return -EREMOTE; 933 934 /* We don't want to mount if someone's just doing a stat - 935 * unless they're stat'ing a directory and appended a '/' to 936 * the name. 937 * 938 * We do, however, want to mount if someone wants to open or 939 * create a file of any type under the mountpoint, wants to 940 * traverse through the mountpoint or wants to open the 941 * mounted directory. Also, autofs may mark negative dentries 942 * as being automount points. These will need the attentions 943 * of the daemon to instantiate them before they can be used. 944 */ 945 if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY | 946 LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) && 947 path->dentry->d_inode) 948 return -EISDIR; 949 950 current->total_link_count++; 951 if (current->total_link_count >= 40) 952 return -ELOOP; 953 954 mnt = path->dentry->d_op->d_automount(path); 955 if (IS_ERR(mnt)) { 956 /* 957 * The filesystem is allowed to return -EISDIR here to indicate 958 * it doesn't want to automount. For instance, autofs would do 959 * this so that its userspace daemon can mount on this dentry. 960 * 961 * However, we can only permit this if it's a terminal point in 962 * the path being looked up; if it wasn't then the remainder of 963 * the path is inaccessible and we should say so. 964 */ 965 if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT)) 966 return -EREMOTE; 967 return PTR_ERR(mnt); 968 } 969 970 if (!mnt) /* mount collision */ 971 return 0; 972 973 if (!*need_mntput) { 974 /* lock_mount() may release path->mnt on error */ 975 mntget(path->mnt); 976 *need_mntput = true; 977 } 978 err = finish_automount(mnt, path); 979 980 switch (err) { 981 case -EBUSY: 982 /* Someone else made a mount here whilst we were busy */ 983 return 0; 984 case 0: 985 path_put(path); 986 path->mnt = mnt; 987 path->dentry = dget(mnt->mnt_root); 988 return 0; 989 default: 990 return err; 991 } 992 993 } 994 995 /* 996 * Handle a dentry that is managed in some way. 997 * - Flagged for transit management (autofs) 998 * - Flagged as mountpoint 999 * - Flagged as automount point 1000 * 1001 * This may only be called in refwalk mode. 1002 * 1003 * Serialization is taken care of in namespace.c 1004 */ 1005 static int follow_managed(struct path *path, unsigned flags) 1006 { 1007 struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */ 1008 unsigned managed; 1009 bool need_mntput = false; 1010 int ret = 0; 1011 1012 /* Given that we're not holding a lock here, we retain the value in a 1013 * local variable for each dentry as we look at it so that we don't see 1014 * the components of that value change under us */ 1015 while (managed = ACCESS_ONCE(path->dentry->d_flags), 1016 managed &= DCACHE_MANAGED_DENTRY, 1017 unlikely(managed != 0)) { 1018 /* Allow the filesystem to manage the transit without i_mutex 1019 * being held. */ 1020 if (managed & DCACHE_MANAGE_TRANSIT) { 1021 BUG_ON(!path->dentry->d_op); 1022 BUG_ON(!path->dentry->d_op->d_manage); 1023 ret = path->dentry->d_op->d_manage(path->dentry, false); 1024 if (ret < 0) 1025 break; 1026 } 1027 1028 /* Transit to a mounted filesystem. */ 1029 if (managed & DCACHE_MOUNTED) { 1030 struct vfsmount *mounted = lookup_mnt(path); 1031 if (mounted) { 1032 dput(path->dentry); 1033 if (need_mntput) 1034 mntput(path->mnt); 1035 path->mnt = mounted; 1036 path->dentry = dget(mounted->mnt_root); 1037 need_mntput = true; 1038 continue; 1039 } 1040 1041 /* Something is mounted on this dentry in another 1042 * namespace and/or whatever was mounted there in this 1043 * namespace got unmounted before we managed to get the 1044 * vfsmount_lock */ 1045 } 1046 1047 /* Handle an automount point */ 1048 if (managed & DCACHE_NEED_AUTOMOUNT) { 1049 ret = follow_automount(path, flags, &need_mntput); 1050 if (ret < 0) 1051 break; 1052 continue; 1053 } 1054 1055 /* We didn't change the current path point */ 1056 break; 1057 } 1058 1059 if (need_mntput && path->mnt == mnt) 1060 mntput(path->mnt); 1061 if (ret == -EISDIR) 1062 ret = 0; 1063 return ret < 0 ? ret : need_mntput; 1064 } 1065 1066 int follow_down_one(struct path *path) 1067 { 1068 struct vfsmount *mounted; 1069 1070 mounted = lookup_mnt(path); 1071 if (mounted) { 1072 dput(path->dentry); 1073 mntput(path->mnt); 1074 path->mnt = mounted; 1075 path->dentry = dget(mounted->mnt_root); 1076 return 1; 1077 } 1078 return 0; 1079 } 1080 1081 static inline bool managed_dentry_might_block(struct dentry *dentry) 1082 { 1083 return (dentry->d_flags & DCACHE_MANAGE_TRANSIT && 1084 dentry->d_op->d_manage(dentry, true) < 0); 1085 } 1086 1087 /* 1088 * Try to skip to top of mountpoint pile in rcuwalk mode. Fail if 1089 * we meet a managed dentry that would need blocking. 1090 */ 1091 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, 1092 struct inode **inode) 1093 { 1094 for (;;) { 1095 struct mount *mounted; 1096 /* 1097 * Don't forget we might have a non-mountpoint managed dentry 1098 * that wants to block transit. 1099 */ 1100 if (unlikely(managed_dentry_might_block(path->dentry))) 1101 return false; 1102 1103 if (!d_mountpoint(path->dentry)) 1104 break; 1105 1106 mounted = __lookup_mnt(path->mnt, path->dentry, 1); 1107 if (!mounted) 1108 break; 1109 path->mnt = &mounted->mnt; 1110 path->dentry = mounted->mnt.mnt_root; 1111 nd->flags |= LOOKUP_JUMPED; 1112 nd->seq = read_seqcount_begin(&path->dentry->d_seq); 1113 /* 1114 * Update the inode too. We don't need to re-check the 1115 * dentry sequence number here after this d_inode read, 1116 * because a mount-point is always pinned. 1117 */ 1118 *inode = path->dentry->d_inode; 1119 } 1120 return true; 1121 } 1122 1123 static void follow_mount_rcu(struct nameidata *nd) 1124 { 1125 while (d_mountpoint(nd->path.dentry)) { 1126 struct mount *mounted; 1127 mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry, 1); 1128 if (!mounted) 1129 break; 1130 nd->path.mnt = &mounted->mnt; 1131 nd->path.dentry = mounted->mnt.mnt_root; 1132 nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); 1133 } 1134 } 1135 1136 static int follow_dotdot_rcu(struct nameidata *nd) 1137 { 1138 set_root_rcu(nd); 1139 1140 while (1) { 1141 if (nd->path.dentry == nd->root.dentry && 1142 nd->path.mnt == nd->root.mnt) { 1143 break; 1144 } 1145 if (nd->path.dentry != nd->path.mnt->mnt_root) { 1146 struct dentry *old = nd->path.dentry; 1147 struct dentry *parent = old->d_parent; 1148 unsigned seq; 1149 1150 seq = read_seqcount_begin(&parent->d_seq); 1151 if (read_seqcount_retry(&old->d_seq, nd->seq)) 1152 goto failed; 1153 nd->path.dentry = parent; 1154 nd->seq = seq; 1155 break; 1156 } 1157 if (!follow_up_rcu(&nd->path)) 1158 break; 1159 nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); 1160 } 1161 follow_mount_rcu(nd); 1162 nd->inode = nd->path.dentry->d_inode; 1163 return 0; 1164 1165 failed: 1166 nd->flags &= ~LOOKUP_RCU; 1167 if (!(nd->flags & LOOKUP_ROOT)) 1168 nd->root.mnt = NULL; 1169 unlock_rcu_walk(); 1170 return -ECHILD; 1171 } 1172 1173 /* 1174 * Follow down to the covering mount currently visible to userspace. At each 1175 * point, the filesystem owning that dentry may be queried as to whether the 1176 * caller is permitted to proceed or not. 1177 */ 1178 int follow_down(struct path *path) 1179 { 1180 unsigned managed; 1181 int ret; 1182 1183 while (managed = ACCESS_ONCE(path->dentry->d_flags), 1184 unlikely(managed & DCACHE_MANAGED_DENTRY)) { 1185 /* Allow the filesystem to manage the transit without i_mutex 1186 * being held. 1187 * 1188 * We indicate to the filesystem if someone is trying to mount 1189 * something here. This gives autofs the chance to deny anyone 1190 * other than its daemon the right to mount on its 1191 * superstructure. 1192 * 1193 * The filesystem may sleep at this point. 1194 */ 1195 if (managed & DCACHE_MANAGE_TRANSIT) { 1196 BUG_ON(!path->dentry->d_op); 1197 BUG_ON(!path->dentry->d_op->d_manage); 1198 ret = path->dentry->d_op->d_manage( 1199 path->dentry, false); 1200 if (ret < 0) 1201 return ret == -EISDIR ? 0 : ret; 1202 } 1203 1204 /* Transit to a mounted filesystem. */ 1205 if (managed & DCACHE_MOUNTED) { 1206 struct vfsmount *mounted = lookup_mnt(path); 1207 if (!mounted) 1208 break; 1209 dput(path->dentry); 1210 mntput(path->mnt); 1211 path->mnt = mounted; 1212 path->dentry = dget(mounted->mnt_root); 1213 continue; 1214 } 1215 1216 /* Don't handle automount points here */ 1217 break; 1218 } 1219 return 0; 1220 } 1221 1222 /* 1223 * Skip to top of mountpoint pile in refwalk mode for follow_dotdot() 1224 */ 1225 static void follow_mount(struct path *path) 1226 { 1227 while (d_mountpoint(path->dentry)) { 1228 struct vfsmount *mounted = lookup_mnt(path); 1229 if (!mounted) 1230 break; 1231 dput(path->dentry); 1232 mntput(path->mnt); 1233 path->mnt = mounted; 1234 path->dentry = dget(mounted->mnt_root); 1235 } 1236 } 1237 1238 static void follow_dotdot(struct nameidata *nd) 1239 { 1240 set_root(nd); 1241 1242 while(1) { 1243 struct dentry *old = nd->path.dentry; 1244 1245 if (nd->path.dentry == nd->root.dentry && 1246 nd->path.mnt == nd->root.mnt) { 1247 break; 1248 } 1249 if (nd->path.dentry != nd->path.mnt->mnt_root) { 1250 /* rare case of legitimate dget_parent()... */ 1251 nd->path.dentry = dget_parent(nd->path.dentry); 1252 dput(old); 1253 break; 1254 } 1255 if (!follow_up(&nd->path)) 1256 break; 1257 } 1258 follow_mount(&nd->path); 1259 nd->inode = nd->path.dentry->d_inode; 1260 } 1261 1262 /* 1263 * This looks up the name in dcache, possibly revalidates the old dentry and 1264 * allocates a new one if not found or not valid. In the need_lookup argument 1265 * returns whether i_op->lookup is necessary. 1266 * 1267 * dir->d_inode->i_mutex must be held 1268 */ 1269 static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir, 1270 unsigned int flags, bool *need_lookup) 1271 { 1272 struct dentry *dentry; 1273 int error; 1274 1275 *need_lookup = false; 1276 dentry = d_lookup(dir, name); 1277 if (dentry) { 1278 if (dentry->d_flags & DCACHE_OP_REVALIDATE) { 1279 error = d_revalidate(dentry, flags); 1280 if (unlikely(error <= 0)) { 1281 if (error < 0) { 1282 dput(dentry); 1283 return ERR_PTR(error); 1284 } else if (!d_invalidate(dentry)) { 1285 dput(dentry); 1286 dentry = NULL; 1287 } 1288 } 1289 } 1290 } 1291 1292 if (!dentry) { 1293 dentry = d_alloc(dir, name); 1294 if (unlikely(!dentry)) 1295 return ERR_PTR(-ENOMEM); 1296 1297 *need_lookup = true; 1298 } 1299 return dentry; 1300 } 1301 1302 /* 1303 * Call i_op->lookup on the dentry. The dentry must be negative but may be 1304 * hashed if it was pouplated with DCACHE_NEED_LOOKUP. 1305 * 1306 * dir->d_inode->i_mutex must be held 1307 */ 1308 static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry, 1309 unsigned int flags) 1310 { 1311 struct dentry *old; 1312 1313 /* Don't create child dentry for a dead directory. */ 1314 if (unlikely(IS_DEADDIR(dir))) { 1315 dput(dentry); 1316 return ERR_PTR(-ENOENT); 1317 } 1318 1319 old = dir->i_op->lookup(dir, dentry, flags); 1320 if (unlikely(old)) { 1321 dput(dentry); 1322 dentry = old; 1323 } 1324 return dentry; 1325 } 1326 1327 static struct dentry *__lookup_hash(struct qstr *name, 1328 struct dentry *base, unsigned int flags) 1329 { 1330 bool need_lookup; 1331 struct dentry *dentry; 1332 1333 dentry = lookup_dcache(name, base, flags, &need_lookup); 1334 if (!need_lookup) 1335 return dentry; 1336 1337 return lookup_real(base->d_inode, dentry, flags); 1338 } 1339 1340 /* 1341 * It's more convoluted than I'd like it to be, but... it's still fairly 1342 * small and for now I'd prefer to have fast path as straight as possible. 1343 * It _is_ time-critical. 1344 */ 1345 static int lookup_fast(struct nameidata *nd, struct qstr *name, 1346 struct path *path, struct inode **inode) 1347 { 1348 struct vfsmount *mnt = nd->path.mnt; 1349 struct dentry *dentry, *parent = nd->path.dentry; 1350 int need_reval = 1; 1351 int status = 1; 1352 int err; 1353 1354 /* 1355 * Rename seqlock is not required here because in the off chance 1356 * of a false negative due to a concurrent rename, we're going to 1357 * do the non-racy lookup, below. 1358 */ 1359 if (nd->flags & LOOKUP_RCU) { 1360 unsigned seq; 1361 dentry = __d_lookup_rcu(parent, name, &seq, nd->inode); 1362 if (!dentry) 1363 goto unlazy; 1364 1365 /* 1366 * This sequence count validates that the inode matches 1367 * the dentry name information from lookup. 1368 */ 1369 *inode = dentry->d_inode; 1370 if (read_seqcount_retry(&dentry->d_seq, seq)) 1371 return -ECHILD; 1372 1373 /* 1374 * This sequence count validates that the parent had no 1375 * changes while we did the lookup of the dentry above. 1376 * 1377 * The memory barrier in read_seqcount_begin of child is 1378 * enough, we can use __read_seqcount_retry here. 1379 */ 1380 if (__read_seqcount_retry(&parent->d_seq, nd->seq)) 1381 return -ECHILD; 1382 nd->seq = seq; 1383 1384 if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) { 1385 status = d_revalidate(dentry, nd->flags); 1386 if (unlikely(status <= 0)) { 1387 if (status != -ECHILD) 1388 need_reval = 0; 1389 goto unlazy; 1390 } 1391 } 1392 path->mnt = mnt; 1393 path->dentry = dentry; 1394 if (unlikely(!__follow_mount_rcu(nd, path, inode))) 1395 goto unlazy; 1396 if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT)) 1397 goto unlazy; 1398 return 0; 1399 unlazy: 1400 if (unlazy_walk(nd, dentry)) 1401 return -ECHILD; 1402 } else { 1403 dentry = __d_lookup(parent, name); 1404 } 1405 1406 if (unlikely(!dentry)) 1407 goto need_lookup; 1408 1409 if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval) 1410 status = d_revalidate(dentry, nd->flags); 1411 if (unlikely(status <= 0)) { 1412 if (status < 0) { 1413 dput(dentry); 1414 return status; 1415 } 1416 if (!d_invalidate(dentry)) { 1417 dput(dentry); 1418 goto need_lookup; 1419 } 1420 } 1421 1422 path->mnt = mnt; 1423 path->dentry = dentry; 1424 err = follow_managed(path, nd->flags); 1425 if (unlikely(err < 0)) { 1426 path_put_conditional(path, nd); 1427 return err; 1428 } 1429 if (err) 1430 nd->flags |= LOOKUP_JUMPED; 1431 *inode = path->dentry->d_inode; 1432 return 0; 1433 1434 need_lookup: 1435 return 1; 1436 } 1437 1438 /* Fast lookup failed, do it the slow way */ 1439 static int lookup_slow(struct nameidata *nd, struct qstr *name, 1440 struct path *path) 1441 { 1442 struct dentry *dentry, *parent; 1443 int err; 1444 1445 parent = nd->path.dentry; 1446 BUG_ON(nd->inode != parent->d_inode); 1447 1448 mutex_lock(&parent->d_inode->i_mutex); 1449 dentry = __lookup_hash(name, parent, nd->flags); 1450 mutex_unlock(&parent->d_inode->i_mutex); 1451 if (IS_ERR(dentry)) 1452 return PTR_ERR(dentry); 1453 path->mnt = nd->path.mnt; 1454 path->dentry = dentry; 1455 err = follow_managed(path, nd->flags); 1456 if (unlikely(err < 0)) { 1457 path_put_conditional(path, nd); 1458 return err; 1459 } 1460 if (err) 1461 nd->flags |= LOOKUP_JUMPED; 1462 return 0; 1463 } 1464 1465 static inline int may_lookup(struct nameidata *nd) 1466 { 1467 if (nd->flags & LOOKUP_RCU) { 1468 int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK); 1469 if (err != -ECHILD) 1470 return err; 1471 if (unlazy_walk(nd, NULL)) 1472 return -ECHILD; 1473 } 1474 return inode_permission(nd->inode, MAY_EXEC); 1475 } 1476 1477 static inline int handle_dots(struct nameidata *nd, int type) 1478 { 1479 if (type == LAST_DOTDOT) { 1480 if (nd->flags & LOOKUP_RCU) { 1481 if (follow_dotdot_rcu(nd)) 1482 return -ECHILD; 1483 } else 1484 follow_dotdot(nd); 1485 } 1486 return 0; 1487 } 1488 1489 static void terminate_walk(struct nameidata *nd) 1490 { 1491 if (!(nd->flags & LOOKUP_RCU)) { 1492 path_put(&nd->path); 1493 } else { 1494 nd->flags &= ~LOOKUP_RCU; 1495 if (!(nd->flags & LOOKUP_ROOT)) 1496 nd->root.mnt = NULL; 1497 unlock_rcu_walk(); 1498 } 1499 } 1500 1501 /* 1502 * Do we need to follow links? We _really_ want to be able 1503 * to do this check without having to look at inode->i_op, 1504 * so we keep a cache of "no, this doesn't need follow_link" 1505 * for the common case. 1506 */ 1507 static inline int should_follow_link(struct inode *inode, int follow) 1508 { 1509 if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) { 1510 if (likely(inode->i_op->follow_link)) 1511 return follow; 1512 1513 /* This gets set once for the inode lifetime */ 1514 spin_lock(&inode->i_lock); 1515 inode->i_opflags |= IOP_NOFOLLOW; 1516 spin_unlock(&inode->i_lock); 1517 } 1518 return 0; 1519 } 1520 1521 static inline int walk_component(struct nameidata *nd, struct path *path, 1522 struct qstr *name, int type, int follow) 1523 { 1524 struct inode *inode; 1525 int err; 1526 /* 1527 * "." and ".." are special - ".." especially so because it has 1528 * to be able to know about the current root directory and 1529 * parent relationships. 1530 */ 1531 if (unlikely(type != LAST_NORM)) 1532 return handle_dots(nd, type); 1533 err = lookup_fast(nd, name, path, &inode); 1534 if (unlikely(err)) { 1535 if (err < 0) 1536 goto out_err; 1537 1538 err = lookup_slow(nd, name, path); 1539 if (err < 0) 1540 goto out_err; 1541 1542 inode = path->dentry->d_inode; 1543 } 1544 err = -ENOENT; 1545 if (!inode) 1546 goto out_path_put; 1547 1548 if (should_follow_link(inode, follow)) { 1549 if (nd->flags & LOOKUP_RCU) { 1550 if (unlikely(unlazy_walk(nd, path->dentry))) { 1551 err = -ECHILD; 1552 goto out_err; 1553 } 1554 } 1555 BUG_ON(inode != path->dentry->d_inode); 1556 return 1; 1557 } 1558 path_to_nameidata(path, nd); 1559 nd->inode = inode; 1560 return 0; 1561 1562 out_path_put: 1563 path_to_nameidata(path, nd); 1564 out_err: 1565 terminate_walk(nd); 1566 return err; 1567 } 1568 1569 /* 1570 * This limits recursive symlink follows to 8, while 1571 * limiting consecutive symlinks to 40. 1572 * 1573 * Without that kind of total limit, nasty chains of consecutive 1574 * symlinks can cause almost arbitrarily long lookups. 1575 */ 1576 static inline int nested_symlink(struct path *path, struct nameidata *nd) 1577 { 1578 int res; 1579 1580 if (unlikely(current->link_count >= MAX_NESTED_LINKS)) { 1581 path_put_conditional(path, nd); 1582 path_put(&nd->path); 1583 return -ELOOP; 1584 } 1585 BUG_ON(nd->depth >= MAX_NESTED_LINKS); 1586 1587 nd->depth++; 1588 current->link_count++; 1589 1590 do { 1591 struct path link = *path; 1592 void *cookie; 1593 1594 res = follow_link(&link, nd, &cookie); 1595 if (res) 1596 break; 1597 res = walk_component(nd, path, &nd->last, 1598 nd->last_type, LOOKUP_FOLLOW); 1599 put_link(nd, &link, cookie); 1600 } while (res > 0); 1601 1602 current->link_count--; 1603 nd->depth--; 1604 return res; 1605 } 1606 1607 /* 1608 * We really don't want to look at inode->i_op->lookup 1609 * when we don't have to. So we keep a cache bit in 1610 * the inode ->i_opflags field that says "yes, we can 1611 * do lookup on this inode". 1612 */ 1613 static inline int can_lookup(struct inode *inode) 1614 { 1615 if (likely(inode->i_opflags & IOP_LOOKUP)) 1616 return 1; 1617 if (likely(!inode->i_op->lookup)) 1618 return 0; 1619 1620 /* We do this once for the lifetime of the inode */ 1621 spin_lock(&inode->i_lock); 1622 inode->i_opflags |= IOP_LOOKUP; 1623 spin_unlock(&inode->i_lock); 1624 return 1; 1625 } 1626 1627 /* 1628 * We can do the critical dentry name comparison and hashing 1629 * operations one word at a time, but we are limited to: 1630 * 1631 * - Architectures with fast unaligned word accesses. We could 1632 * do a "get_unaligned()" if this helps and is sufficiently 1633 * fast. 1634 * 1635 * - Little-endian machines (so that we can generate the mask 1636 * of low bytes efficiently). Again, we *could* do a byte 1637 * swapping load on big-endian architectures if that is not 1638 * expensive enough to make the optimization worthless. 1639 * 1640 * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we 1641 * do not trap on the (extremely unlikely) case of a page 1642 * crossing operation. 1643 * 1644 * - Furthermore, we need an efficient 64-bit compile for the 1645 * 64-bit case in order to generate the "number of bytes in 1646 * the final mask". Again, that could be replaced with a 1647 * efficient population count instruction or similar. 1648 */ 1649 #ifdef CONFIG_DCACHE_WORD_ACCESS 1650 1651 #include <asm/word-at-a-time.h> 1652 1653 #ifdef CONFIG_64BIT 1654 1655 static inline unsigned int fold_hash(unsigned long hash) 1656 { 1657 hash += hash >> (8*sizeof(int)); 1658 return hash; 1659 } 1660 1661 #else /* 32-bit case */ 1662 1663 #define fold_hash(x) (x) 1664 1665 #endif 1666 1667 unsigned int full_name_hash(const unsigned char *name, unsigned int len) 1668 { 1669 unsigned long a, mask; 1670 unsigned long hash = 0; 1671 1672 for (;;) { 1673 a = load_unaligned_zeropad(name); 1674 if (len < sizeof(unsigned long)) 1675 break; 1676 hash += a; 1677 hash *= 9; 1678 name += sizeof(unsigned long); 1679 len -= sizeof(unsigned long); 1680 if (!len) 1681 goto done; 1682 } 1683 mask = ~(~0ul << len*8); 1684 hash += mask & a; 1685 done: 1686 return fold_hash(hash); 1687 } 1688 EXPORT_SYMBOL(full_name_hash); 1689 1690 /* 1691 * Calculate the length and hash of the path component, and 1692 * return the length of the component; 1693 */ 1694 static inline unsigned long hash_name(const char *name, unsigned int *hashp) 1695 { 1696 unsigned long a, b, adata, bdata, mask, hash, len; 1697 const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; 1698 1699 hash = a = 0; 1700 len = -sizeof(unsigned long); 1701 do { 1702 hash = (hash + a) * 9; 1703 len += sizeof(unsigned long); 1704 a = load_unaligned_zeropad(name+len); 1705 b = a ^ REPEAT_BYTE('/'); 1706 } while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants))); 1707 1708 adata = prep_zero_mask(a, adata, &constants); 1709 bdata = prep_zero_mask(b, bdata, &constants); 1710 1711 mask = create_zero_mask(adata | bdata); 1712 1713 hash += a & zero_bytemask(mask); 1714 *hashp = fold_hash(hash); 1715 1716 return len + find_zero(mask); 1717 } 1718 1719 #else 1720 1721 unsigned int full_name_hash(const unsigned char *name, unsigned int len) 1722 { 1723 unsigned long hash = init_name_hash(); 1724 while (len--) 1725 hash = partial_name_hash(*name++, hash); 1726 return end_name_hash(hash); 1727 } 1728 EXPORT_SYMBOL(full_name_hash); 1729 1730 /* 1731 * We know there's a real path component here of at least 1732 * one character. 1733 */ 1734 static inline unsigned long hash_name(const char *name, unsigned int *hashp) 1735 { 1736 unsigned long hash = init_name_hash(); 1737 unsigned long len = 0, c; 1738 1739 c = (unsigned char)*name; 1740 do { 1741 len++; 1742 hash = partial_name_hash(c, hash); 1743 c = (unsigned char)name[len]; 1744 } while (c && c != '/'); 1745 *hashp = end_name_hash(hash); 1746 return len; 1747 } 1748 1749 #endif 1750 1751 /* 1752 * Name resolution. 1753 * This is the basic name resolution function, turning a pathname into 1754 * the final dentry. We expect 'base' to be positive and a directory. 1755 * 1756 * Returns 0 and nd will have valid dentry and mnt on success. 1757 * Returns error and drops reference to input namei data on failure. 1758 */ 1759 static int link_path_walk(const char *name, struct nameidata *nd) 1760 { 1761 struct path next; 1762 int err; 1763 1764 while (*name=='/') 1765 name++; 1766 if (!*name) 1767 return 0; 1768 1769 /* At this point we know we have a real path component. */ 1770 for(;;) { 1771 struct qstr this; 1772 long len; 1773 int type; 1774 1775 err = may_lookup(nd); 1776 if (err) 1777 break; 1778 1779 len = hash_name(name, &this.hash); 1780 this.name = name; 1781 this.len = len; 1782 1783 type = LAST_NORM; 1784 if (name[0] == '.') switch (len) { 1785 case 2: 1786 if (name[1] == '.') { 1787 type = LAST_DOTDOT; 1788 nd->flags |= LOOKUP_JUMPED; 1789 } 1790 break; 1791 case 1: 1792 type = LAST_DOT; 1793 } 1794 if (likely(type == LAST_NORM)) { 1795 struct dentry *parent = nd->path.dentry; 1796 nd->flags &= ~LOOKUP_JUMPED; 1797 if (unlikely(parent->d_flags & DCACHE_OP_HASH)) { 1798 err = parent->d_op->d_hash(parent, nd->inode, 1799 &this); 1800 if (err < 0) 1801 break; 1802 } 1803 } 1804 1805 if (!name[len]) 1806 goto last_component; 1807 /* 1808 * If it wasn't NUL, we know it was '/'. Skip that 1809 * slash, and continue until no more slashes. 1810 */ 1811 do { 1812 len++; 1813 } while (unlikely(name[len] == '/')); 1814 if (!name[len]) 1815 goto last_component; 1816 name += len; 1817 1818 err = walk_component(nd, &next, &this, type, LOOKUP_FOLLOW); 1819 if (err < 0) 1820 return err; 1821 1822 if (err) { 1823 err = nested_symlink(&next, nd); 1824 if (err) 1825 return err; 1826 } 1827 if (can_lookup(nd->inode)) 1828 continue; 1829 err = -ENOTDIR; 1830 break; 1831 /* here ends the main loop */ 1832 1833 last_component: 1834 nd->last = this; 1835 nd->last_type = type; 1836 return 0; 1837 } 1838 terminate_walk(nd); 1839 return err; 1840 } 1841 1842 static int path_init(int dfd, const char *name, unsigned int flags, 1843 struct nameidata *nd, struct file **fp) 1844 { 1845 int retval = 0; 1846 1847 nd->last_type = LAST_ROOT; /* if there are only slashes... */ 1848 nd->flags = flags | LOOKUP_JUMPED; 1849 nd->depth = 0; 1850 if (flags & LOOKUP_ROOT) { 1851 struct inode *inode = nd->root.dentry->d_inode; 1852 if (*name) { 1853 if (!can_lookup(inode)) 1854 return -ENOTDIR; 1855 retval = inode_permission(inode, MAY_EXEC); 1856 if (retval) 1857 return retval; 1858 } 1859 nd->path = nd->root; 1860 nd->inode = inode; 1861 if (flags & LOOKUP_RCU) { 1862 lock_rcu_walk(); 1863 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); 1864 } else { 1865 path_get(&nd->path); 1866 } 1867 return 0; 1868 } 1869 1870 nd->root.mnt = NULL; 1871 1872 if (*name=='/') { 1873 if (flags & LOOKUP_RCU) { 1874 lock_rcu_walk(); 1875 set_root_rcu(nd); 1876 } else { 1877 set_root(nd); 1878 path_get(&nd->root); 1879 } 1880 nd->path = nd->root; 1881 } else if (dfd == AT_FDCWD) { 1882 if (flags & LOOKUP_RCU) { 1883 struct fs_struct *fs = current->fs; 1884 unsigned seq; 1885 1886 lock_rcu_walk(); 1887 1888 do { 1889 seq = read_seqcount_begin(&fs->seq); 1890 nd->path = fs->pwd; 1891 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); 1892 } while (read_seqcount_retry(&fs->seq, seq)); 1893 } else { 1894 get_fs_pwd(current->fs, &nd->path); 1895 } 1896 } else { 1897 /* Caller must check execute permissions on the starting path component */ 1898 struct fd f = fdget_raw(dfd); 1899 struct dentry *dentry; 1900 1901 if (!f.file) 1902 return -EBADF; 1903 1904 dentry = f.file->f_path.dentry; 1905 1906 if (*name) { 1907 if (!can_lookup(dentry->d_inode)) { 1908 fdput(f); 1909 return -ENOTDIR; 1910 } 1911 } 1912 1913 nd->path = f.file->f_path; 1914 if (flags & LOOKUP_RCU) { 1915 if (f.need_put) 1916 *fp = f.file; 1917 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); 1918 lock_rcu_walk(); 1919 } else { 1920 path_get(&nd->path); 1921 fdput(f); 1922 } 1923 } 1924 1925 nd->inode = nd->path.dentry->d_inode; 1926 return 0; 1927 } 1928 1929 static inline int lookup_last(struct nameidata *nd, struct path *path) 1930 { 1931 if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len]) 1932 nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; 1933 1934 nd->flags &= ~LOOKUP_PARENT; 1935 return walk_component(nd, path, &nd->last, nd->last_type, 1936 nd->flags & LOOKUP_FOLLOW); 1937 } 1938 1939 /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */ 1940 static int path_lookupat(int dfd, const char *name, 1941 unsigned int flags, struct nameidata *nd) 1942 { 1943 struct file *base = NULL; 1944 struct path path; 1945 int err; 1946 1947 /* 1948 * Path walking is largely split up into 2 different synchronisation 1949 * schemes, rcu-walk and ref-walk (explained in 1950 * Documentation/filesystems/path-lookup.txt). These share much of the 1951 * path walk code, but some things particularly setup, cleanup, and 1952 * following mounts are sufficiently divergent that functions are 1953 * duplicated. Typically there is a function foo(), and its RCU 1954 * analogue, foo_rcu(). 1955 * 1956 * -ECHILD is the error number of choice (just to avoid clashes) that 1957 * is returned if some aspect of an rcu-walk fails. Such an error must 1958 * be handled by restarting a traditional ref-walk (which will always 1959 * be able to complete). 1960 */ 1961 err = path_init(dfd, name, flags | LOOKUP_PARENT, nd, &base); 1962 1963 if (unlikely(err)) 1964 return err; 1965 1966 current->total_link_count = 0; 1967 err = link_path_walk(name, nd); 1968 1969 if (!err && !(flags & LOOKUP_PARENT)) { 1970 err = lookup_last(nd, &path); 1971 while (err > 0) { 1972 void *cookie; 1973 struct path link = path; 1974 err = may_follow_link(&link, nd); 1975 if (unlikely(err)) 1976 break; 1977 nd->flags |= LOOKUP_PARENT; 1978 err = follow_link(&link, nd, &cookie); 1979 if (err) 1980 break; 1981 err = lookup_last(nd, &path); 1982 put_link(nd, &link, cookie); 1983 } 1984 } 1985 1986 if (!err) 1987 err = complete_walk(nd); 1988 1989 if (!err && nd->flags & LOOKUP_DIRECTORY) { 1990 if (!nd->inode->i_op->lookup) { 1991 path_put(&nd->path); 1992 err = -ENOTDIR; 1993 } 1994 } 1995 1996 if (base) 1997 fput(base); 1998 1999 if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { 2000 path_put(&nd->root); 2001 nd->root.mnt = NULL; 2002 } 2003 return err; 2004 } 2005 2006 static int filename_lookup(int dfd, struct filename *name, 2007 unsigned int flags, struct nameidata *nd) 2008 { 2009 int retval = path_lookupat(dfd, name->name, flags | LOOKUP_RCU, nd); 2010 if (unlikely(retval == -ECHILD)) 2011 retval = path_lookupat(dfd, name->name, flags, nd); 2012 if (unlikely(retval == -ESTALE)) 2013 retval = path_lookupat(dfd, name->name, 2014 flags | LOOKUP_REVAL, nd); 2015 2016 if (likely(!retval)) 2017 audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT); 2018 return retval; 2019 } 2020 2021 static int do_path_lookup(int dfd, const char *name, 2022 unsigned int flags, struct nameidata *nd) 2023 { 2024 struct filename filename = { .name = name }; 2025 2026 return filename_lookup(dfd, &filename, flags, nd); 2027 } 2028 2029 /* does lookup, returns the object with parent locked */ 2030 struct dentry *kern_path_locked(const char *name, struct path *path) 2031 { 2032 struct nameidata nd; 2033 struct dentry *d; 2034 int err = do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, &nd); 2035 if (err) 2036 return ERR_PTR(err); 2037 if (nd.last_type != LAST_NORM) { 2038 path_put(&nd.path); 2039 return ERR_PTR(-EINVAL); 2040 } 2041 mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); 2042 d = __lookup_hash(&nd.last, nd.path.dentry, 0); 2043 if (IS_ERR(d)) { 2044 mutex_unlock(&nd.path.dentry->d_inode->i_mutex); 2045 path_put(&nd.path); 2046 return d; 2047 } 2048 *path = nd.path; 2049 return d; 2050 } 2051 2052 int kern_path(const char *name, unsigned int flags, struct path *path) 2053 { 2054 struct nameidata nd; 2055 int res = do_path_lookup(AT_FDCWD, name, flags, &nd); 2056 if (!res) 2057 *path = nd.path; 2058 return res; 2059 } 2060 2061 /** 2062 * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair 2063 * @dentry: pointer to dentry of the base directory 2064 * @mnt: pointer to vfs mount of the base directory 2065 * @name: pointer to file name 2066 * @flags: lookup flags 2067 * @path: pointer to struct path to fill 2068 */ 2069 int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, 2070 const char *name, unsigned int flags, 2071 struct path *path) 2072 { 2073 struct nameidata nd; 2074 int err; 2075 nd.root.dentry = dentry; 2076 nd.root.mnt = mnt; 2077 BUG_ON(flags & LOOKUP_PARENT); 2078 /* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */ 2079 err = do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, &nd); 2080 if (!err) 2081 *path = nd.path; 2082 return err; 2083 } 2084 2085 /* 2086 * Restricted form of lookup. Doesn't follow links, single-component only, 2087 * needs parent already locked. Doesn't follow mounts. 2088 * SMP-safe. 2089 */ 2090 static struct dentry *lookup_hash(struct nameidata *nd) 2091 { 2092 return __lookup_hash(&nd->last, nd->path.dentry, nd->flags); 2093 } 2094 2095 /** 2096 * lookup_one_len - filesystem helper to lookup single pathname component 2097 * @name: pathname component to lookup 2098 * @base: base directory to lookup from 2099 * @len: maximum length @len should be interpreted to 2100 * 2101 * Note that this routine is purely a helper for filesystem usage and should 2102 * not be called by generic code. Also note that by using this function the 2103 * nameidata argument is passed to the filesystem methods and a filesystem 2104 * using this helper needs to be prepared for that. 2105 */ 2106 struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) 2107 { 2108 struct qstr this; 2109 unsigned int c; 2110 int err; 2111 2112 WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex)); 2113 2114 this.name = name; 2115 this.len = len; 2116 this.hash = full_name_hash(name, len); 2117 if (!len) 2118 return ERR_PTR(-EACCES); 2119 2120 if (unlikely(name[0] == '.')) { 2121 if (len < 2 || (len == 2 && name[1] == '.')) 2122 return ERR_PTR(-EACCES); 2123 } 2124 2125 while (len--) { 2126 c = *(const unsigned char *)name++; 2127 if (c == '/' || c == '\0') 2128 return ERR_PTR(-EACCES); 2129 } 2130 /* 2131 * See if the low-level filesystem might want 2132 * to use its own hash.. 2133 */ 2134 if (base->d_flags & DCACHE_OP_HASH) { 2135 int err = base->d_op->d_hash(base, base->d_inode, &this); 2136 if (err < 0) 2137 return ERR_PTR(err); 2138 } 2139 2140 err = inode_permission(base->d_inode, MAY_EXEC); 2141 if (err) 2142 return ERR_PTR(err); 2143 2144 return __lookup_hash(&this, base, 0); 2145 } 2146 2147 int user_path_at_empty(int dfd, const char __user *name, unsigned flags, 2148 struct path *path, int *empty) 2149 { 2150 struct nameidata nd; 2151 struct filename *tmp = getname_flags(name, flags, empty); 2152 int err = PTR_ERR(tmp); 2153 if (!IS_ERR(tmp)) { 2154 2155 BUG_ON(flags & LOOKUP_PARENT); 2156 2157 err = filename_lookup(dfd, tmp, flags, &nd); 2158 putname(tmp); 2159 if (!err) 2160 *path = nd.path; 2161 } 2162 return err; 2163 } 2164 2165 int user_path_at(int dfd, const char __user *name, unsigned flags, 2166 struct path *path) 2167 { 2168 return user_path_at_empty(dfd, name, flags, path, NULL); 2169 } 2170 2171 /* 2172 * NB: most callers don't do anything directly with the reference to the 2173 * to struct filename, but the nd->last pointer points into the name string 2174 * allocated by getname. So we must hold the reference to it until all 2175 * path-walking is complete. 2176 */ 2177 static struct filename * 2178 user_path_parent(int dfd, const char __user *path, struct nameidata *nd, 2179 unsigned int flags) 2180 { 2181 struct filename *s = getname(path); 2182 int error; 2183 2184 /* only LOOKUP_REVAL is allowed in extra flags */ 2185 flags &= LOOKUP_REVAL; 2186 2187 if (IS_ERR(s)) 2188 return s; 2189 2190 error = filename_lookup(dfd, s, flags | LOOKUP_PARENT, nd); 2191 if (error) { 2192 putname(s); 2193 return ERR_PTR(error); 2194 } 2195 2196 return s; 2197 } 2198 2199 /* 2200 * It's inline, so penalty for filesystems that don't use sticky bit is 2201 * minimal. 2202 */ 2203 static inline int check_sticky(struct inode *dir, struct inode *inode) 2204 { 2205 kuid_t fsuid = current_fsuid(); 2206 2207 if (!(dir->i_mode & S_ISVTX)) 2208 return 0; 2209 if (uid_eq(inode->i_uid, fsuid)) 2210 return 0; 2211 if (uid_eq(dir->i_uid, fsuid)) 2212 return 0; 2213 return !inode_capable(inode, CAP_FOWNER); 2214 } 2215 2216 /* 2217 * Check whether we can remove a link victim from directory dir, check 2218 * whether the type of victim is right. 2219 * 1. We can't do it if dir is read-only (done in permission()) 2220 * 2. We should have write and exec permissions on dir 2221 * 3. We can't remove anything from append-only dir 2222 * 4. We can't do anything with immutable dir (done in permission()) 2223 * 5. If the sticky bit on dir is set we should either 2224 * a. be owner of dir, or 2225 * b. be owner of victim, or 2226 * c. have CAP_FOWNER capability 2227 * 6. If the victim is append-only or immutable we can't do antyhing with 2228 * links pointing to it. 2229 * 7. If we were asked to remove a directory and victim isn't one - ENOTDIR. 2230 * 8. If we were asked to remove a non-directory and victim isn't one - EISDIR. 2231 * 9. We can't remove a root or mountpoint. 2232 * 10. We don't allow removal of NFS sillyrenamed files; it's handled by 2233 * nfs_async_unlink(). 2234 */ 2235 static int may_delete(struct inode *dir,struct dentry *victim,int isdir) 2236 { 2237 int error; 2238 2239 if (!victim->d_inode) 2240 return -ENOENT; 2241 2242 BUG_ON(victim->d_parent->d_inode != dir); 2243 audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE); 2244 2245 error = inode_permission(dir, MAY_WRITE | MAY_EXEC); 2246 if (error) 2247 return error; 2248 if (IS_APPEND(dir)) 2249 return -EPERM; 2250 if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)|| 2251 IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode)) 2252 return -EPERM; 2253 if (isdir) { 2254 if (!S_ISDIR(victim->d_inode->i_mode)) 2255 return -ENOTDIR; 2256 if (IS_ROOT(victim)) 2257 return -EBUSY; 2258 } else if (S_ISDIR(victim->d_inode->i_mode)) 2259 return -EISDIR; 2260 if (IS_DEADDIR(dir)) 2261 return -ENOENT; 2262 if (victim->d_flags & DCACHE_NFSFS_RENAMED) 2263 return -EBUSY; 2264 return 0; 2265 } 2266 2267 /* Check whether we can create an object with dentry child in directory 2268 * dir. 2269 * 1. We can't do it if child already exists (open has special treatment for 2270 * this case, but since we are inlined it's OK) 2271 * 2. We can't do it if dir is read-only (done in permission()) 2272 * 3. We should have write and exec permissions on dir 2273 * 4. We can't do it if dir is immutable (done in permission()) 2274 */ 2275 static inline int may_create(struct inode *dir, struct dentry *child) 2276 { 2277 if (child->d_inode) 2278 return -EEXIST; 2279 if (IS_DEADDIR(dir)) 2280 return -ENOENT; 2281 return inode_permission(dir, MAY_WRITE | MAY_EXEC); 2282 } 2283 2284 /* 2285 * p1 and p2 should be directories on the same fs. 2286 */ 2287 struct dentry *lock_rename(struct dentry *p1, struct dentry *p2) 2288 { 2289 struct dentry *p; 2290 2291 if (p1 == p2) { 2292 mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); 2293 return NULL; 2294 } 2295 2296 mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex); 2297 2298 p = d_ancestor(p2, p1); 2299 if (p) { 2300 mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT); 2301 mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD); 2302 return p; 2303 } 2304 2305 p = d_ancestor(p1, p2); 2306 if (p) { 2307 mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); 2308 mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD); 2309 return p; 2310 } 2311 2312 mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); 2313 mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD); 2314 return NULL; 2315 } 2316 2317 void unlock_rename(struct dentry *p1, struct dentry *p2) 2318 { 2319 mutex_unlock(&p1->d_inode->i_mutex); 2320 if (p1 != p2) { 2321 mutex_unlock(&p2->d_inode->i_mutex); 2322 mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex); 2323 } 2324 } 2325 2326 int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, 2327 bool want_excl) 2328 { 2329 int error = may_create(dir, dentry); 2330 if (error) 2331 return error; 2332 2333 if (!dir->i_op->create) 2334 return -EACCES; /* shouldn't it be ENOSYS? */ 2335 mode &= S_IALLUGO; 2336 mode |= S_IFREG; 2337 error = security_inode_create(dir, dentry, mode); 2338 if (error) 2339 return error; 2340 error = dir->i_op->create(dir, dentry, mode, want_excl); 2341 if (!error) 2342 fsnotify_create(dir, dentry); 2343 return error; 2344 } 2345 2346 static int may_open(struct path *path, int acc_mode, int flag) 2347 { 2348 struct dentry *dentry = path->dentry; 2349 struct inode *inode = dentry->d_inode; 2350 int error; 2351 2352 /* O_PATH? */ 2353 if (!acc_mode) 2354 return 0; 2355 2356 if (!inode) 2357 return -ENOENT; 2358 2359 switch (inode->i_mode & S_IFMT) { 2360 case S_IFLNK: 2361 return -ELOOP; 2362 case S_IFDIR: 2363 if (acc_mode & MAY_WRITE) 2364 return -EISDIR; 2365 break; 2366 case S_IFBLK: 2367 case S_IFCHR: 2368 if (path->mnt->mnt_flags & MNT_NODEV) 2369 return -EACCES; 2370 /*FALLTHRU*/ 2371 case S_IFIFO: 2372 case S_IFSOCK: 2373 flag &= ~O_TRUNC; 2374 break; 2375 } 2376 2377 error = inode_permission(inode, acc_mode); 2378 if (error) 2379 return error; 2380 2381 /* 2382 * An append-only file must be opened in append mode for writing. 2383 */ 2384 if (IS_APPEND(inode)) { 2385 if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND)) 2386 return -EPERM; 2387 if (flag & O_TRUNC) 2388 return -EPERM; 2389 } 2390 2391 /* O_NOATIME can only be set by the owner or superuser */ 2392 if (flag & O_NOATIME && !inode_owner_or_capable(inode)) 2393 return -EPERM; 2394 2395 return 0; 2396 } 2397 2398 static int handle_truncate(struct file *filp) 2399 { 2400 struct path *path = &filp->f_path; 2401 struct inode *inode = path->dentry->d_inode; 2402 int error = get_write_access(inode); 2403 if (error) 2404 return error; 2405 /* 2406 * Refuse to truncate files with mandatory locks held on them. 2407 */ 2408 error = locks_verify_locked(inode); 2409 if (!error) 2410 error = security_path_truncate(path); 2411 if (!error) { 2412 error = do_truncate(path->dentry, 0, 2413 ATTR_MTIME|ATTR_CTIME|ATTR_OPEN, 2414 filp); 2415 } 2416 put_write_access(inode); 2417 return error; 2418 } 2419 2420 static inline int open_to_namei_flags(int flag) 2421 { 2422 if ((flag & O_ACCMODE) == 3) 2423 flag--; 2424 return flag; 2425 } 2426 2427 static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode) 2428 { 2429 int error = security_path_mknod(dir, dentry, mode, 0); 2430 if (error) 2431 return error; 2432 2433 error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC); 2434 if (error) 2435 return error; 2436 2437 return security_inode_create(dir->dentry->d_inode, dentry, mode); 2438 } 2439 2440 /* 2441 * Attempt to atomically look up, create and open a file from a negative 2442 * dentry. 2443 * 2444 * Returns 0 if successful. The file will have been created and attached to 2445 * @file by the filesystem calling finish_open(). 2446 * 2447 * Returns 1 if the file was looked up only or didn't need creating. The 2448 * caller will need to perform the open themselves. @path will have been 2449 * updated to point to the new dentry. This may be negative. 2450 * 2451 * Returns an error code otherwise. 2452 */ 2453 static int atomic_open(struct nameidata *nd, struct dentry *dentry, 2454 struct path *path, struct file *file, 2455 const struct open_flags *op, 2456 bool got_write, bool need_lookup, 2457 int *opened) 2458 { 2459 struct inode *dir = nd->path.dentry->d_inode; 2460 unsigned open_flag = open_to_namei_flags(op->open_flag); 2461 umode_t mode; 2462 int error; 2463 int acc_mode; 2464 int create_error = 0; 2465 struct dentry *const DENTRY_NOT_SET = (void *) -1UL; 2466 2467 BUG_ON(dentry->d_inode); 2468 2469 /* Don't create child dentry for a dead directory. */ 2470 if (unlikely(IS_DEADDIR(dir))) { 2471 error = -ENOENT; 2472 goto out; 2473 } 2474 2475 mode = op->mode; 2476 if ((open_flag & O_CREAT) && !IS_POSIXACL(dir)) 2477 mode &= ~current_umask(); 2478 2479 if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT)) { 2480 open_flag &= ~O_TRUNC; 2481 *opened |= FILE_CREATED; 2482 } 2483 2484 /* 2485 * Checking write permission is tricky, bacuse we don't know if we are 2486 * going to actually need it: O_CREAT opens should work as long as the 2487 * file exists. But checking existence breaks atomicity. The trick is 2488 * to check access and if not granted clear O_CREAT from the flags. 2489 * 2490 * Another problem is returing the "right" error value (e.g. for an 2491 * O_EXCL open we want to return EEXIST not EROFS). 2492 */ 2493 if (((open_flag & (O_CREAT | O_TRUNC)) || 2494 (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) { 2495 if (!(open_flag & O_CREAT)) { 2496 /* 2497 * No O_CREATE -> atomicity not a requirement -> fall 2498 * back to lookup + open 2499 */ 2500 goto no_open; 2501 } else if (open_flag & (O_EXCL | O_TRUNC)) { 2502 /* Fall back and fail with the right error */ 2503 create_error = -EROFS; 2504 goto no_open; 2505 } else { 2506 /* No side effects, safe to clear O_CREAT */ 2507 create_error = -EROFS; 2508 open_flag &= ~O_CREAT; 2509 } 2510 } 2511 2512 if (open_flag & O_CREAT) { 2513 error = may_o_create(&nd->path, dentry, mode); 2514 if (error) { 2515 create_error = error; 2516 if (open_flag & O_EXCL) 2517 goto no_open; 2518 open_flag &= ~O_CREAT; 2519 } 2520 } 2521 2522 if (nd->flags & LOOKUP_DIRECTORY) 2523 open_flag |= O_DIRECTORY; 2524 2525 file->f_path.dentry = DENTRY_NOT_SET; 2526 file->f_path.mnt = nd->path.mnt; 2527 error = dir->i_op->atomic_open(dir, dentry, file, open_flag, mode, 2528 opened); 2529 if (error < 0) { 2530 if (create_error && error == -ENOENT) 2531 error = create_error; 2532 goto out; 2533 } 2534 2535 acc_mode = op->acc_mode; 2536 if (*opened & FILE_CREATED) { 2537 fsnotify_create(dir, dentry); 2538 acc_mode = MAY_OPEN; 2539 } 2540 2541 if (error) { /* returned 1, that is */ 2542 if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) { 2543 error = -EIO; 2544 goto out; 2545 } 2546 if (file->f_path.dentry) { 2547 dput(dentry); 2548 dentry = file->f_path.dentry; 2549 } 2550 if (create_error && dentry->d_inode == NULL) { 2551 error = create_error; 2552 goto out; 2553 } 2554 goto looked_up; 2555 } 2556 2557 /* 2558 * We didn't have the inode before the open, so check open permission 2559 * here. 2560 */ 2561 error = may_open(&file->f_path, acc_mode, open_flag); 2562 if (error) 2563 fput(file); 2564 2565 out: 2566 dput(dentry); 2567 return error; 2568 2569 no_open: 2570 if (need_lookup) { 2571 dentry = lookup_real(dir, dentry, nd->flags); 2572 if (IS_ERR(dentry)) 2573 return PTR_ERR(dentry); 2574 2575 if (create_error) { 2576 int open_flag = op->open_flag; 2577 2578 error = create_error; 2579 if ((open_flag & O_EXCL)) { 2580 if (!dentry->d_inode) 2581 goto out; 2582 } else if (!dentry->d_inode) { 2583 goto out; 2584 } else if ((open_flag & O_TRUNC) && 2585 S_ISREG(dentry->d_inode->i_mode)) { 2586 goto out; 2587 } 2588 /* will fail later, go on to get the right error */ 2589 } 2590 } 2591 looked_up: 2592 path->dentry = dentry; 2593 path->mnt = nd->path.mnt; 2594 return 1; 2595 } 2596 2597 /* 2598 * Look up and maybe create and open the last component. 2599 * 2600 * Must be called with i_mutex held on parent. 2601 * 2602 * Returns 0 if the file was successfully atomically created (if necessary) and 2603 * opened. In this case the file will be returned attached to @file. 2604 * 2605 * Returns 1 if the file was not completely opened at this time, though lookups 2606 * and creations will have been performed and the dentry returned in @path will 2607 * be positive upon return if O_CREAT was specified. If O_CREAT wasn't 2608 * specified then a negative dentry may be returned. 2609 * 2610 * An error code is returned otherwise. 2611 * 2612 * FILE_CREATE will be set in @*opened if the dentry was created and will be 2613 * cleared otherwise prior to returning. 2614 */ 2615 static int lookup_open(struct nameidata *nd, struct path *path, 2616 struct file *file, 2617 const struct open_flags *op, 2618 bool got_write, int *opened) 2619 { 2620 struct dentry *dir = nd->path.dentry; 2621 struct inode *dir_inode = dir->d_inode; 2622 struct dentry *dentry; 2623 int error; 2624 bool need_lookup; 2625 2626 *opened &= ~FILE_CREATED; 2627 dentry = lookup_dcache(&nd->last, dir, nd->flags, &need_lookup); 2628 if (IS_ERR(dentry)) 2629 return PTR_ERR(dentry); 2630 2631 /* Cached positive dentry: will open in f_op->open */ 2632 if (!need_lookup && dentry->d_inode) 2633 goto out_no_open; 2634 2635 if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) { 2636 return atomic_open(nd, dentry, path, file, op, got_write, 2637 need_lookup, opened); 2638 } 2639 2640 if (need_lookup) { 2641 BUG_ON(dentry->d_inode); 2642 2643 dentry = lookup_real(dir_inode, dentry, nd->flags); 2644 if (IS_ERR(dentry)) 2645 return PTR_ERR(dentry); 2646 } 2647 2648 /* Negative dentry, just create the file */ 2649 if (!dentry->d_inode && (op->open_flag & O_CREAT)) { 2650 umode_t mode = op->mode; 2651 if (!IS_POSIXACL(dir->d_inode)) 2652 mode &= ~current_umask(); 2653 /* 2654 * This write is needed to ensure that a 2655 * rw->ro transition does not occur between 2656 * the time when the file is created and when 2657 * a permanent write count is taken through 2658 * the 'struct file' in finish_open(). 2659 */ 2660 if (!got_write) { 2661 error = -EROFS; 2662 goto out_dput; 2663 } 2664 *opened |= FILE_CREATED; 2665 error = security_path_mknod(&nd->path, dentry, mode, 0); 2666 if (error) 2667 goto out_dput; 2668 error = vfs_create(dir->d_inode, dentry, mode, 2669 nd->flags & LOOKUP_EXCL); 2670 if (error) 2671 goto out_dput; 2672 } 2673 out_no_open: 2674 path->dentry = dentry; 2675 path->mnt = nd->path.mnt; 2676 return 1; 2677 2678 out_dput: 2679 dput(dentry); 2680 return error; 2681 } 2682 2683 /* 2684 * Handle the last step of open() 2685 */ 2686 static int do_last(struct nameidata *nd, struct path *path, 2687 struct file *file, const struct open_flags *op, 2688 int *opened, struct filename *name) 2689 { 2690 struct dentry *dir = nd->path.dentry; 2691 int open_flag = op->open_flag; 2692 bool will_truncate = (open_flag & O_TRUNC) != 0; 2693 bool got_write = false; 2694 int acc_mode = op->acc_mode; 2695 struct inode *inode; 2696 bool symlink_ok = false; 2697 struct path save_parent = { .dentry = NULL, .mnt = NULL }; 2698 bool retried = false; 2699 int error; 2700 2701 nd->flags &= ~LOOKUP_PARENT; 2702 nd->flags |= op->intent; 2703 2704 switch (nd->last_type) { 2705 case LAST_DOTDOT: 2706 case LAST_DOT: 2707 error = handle_dots(nd, nd->last_type); 2708 if (error) 2709 return error; 2710 /* fallthrough */ 2711 case LAST_ROOT: 2712 error = complete_walk(nd); 2713 if (error) 2714 return error; 2715 audit_inode(name, nd->path.dentry, 0); 2716 if (open_flag & O_CREAT) { 2717 error = -EISDIR; 2718 goto out; 2719 } 2720 goto finish_open; 2721 case LAST_BIND: 2722 error = complete_walk(nd); 2723 if (error) 2724 return error; 2725 audit_inode(name, dir, 0); 2726 goto finish_open; 2727 } 2728 2729 if (!(open_flag & O_CREAT)) { 2730 if (nd->last.name[nd->last.len]) 2731 nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; 2732 if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW)) 2733 symlink_ok = true; 2734 /* we _can_ be in RCU mode here */ 2735 error = lookup_fast(nd, &nd->last, path, &inode); 2736 if (likely(!error)) 2737 goto finish_lookup; 2738 2739 if (error < 0) 2740 goto out; 2741 2742 BUG_ON(nd->inode != dir->d_inode); 2743 } else { 2744 /* create side of things */ 2745 /* 2746 * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED 2747 * has been cleared when we got to the last component we are 2748 * about to look up 2749 */ 2750 error = complete_walk(nd); 2751 if (error) 2752 return error; 2753 2754 audit_inode(name, dir, 0); 2755 error = -EISDIR; 2756 /* trailing slashes? */ 2757 if (nd->last.name[nd->last.len]) 2758 goto out; 2759 } 2760 2761 retry_lookup: 2762 if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) { 2763 error = mnt_want_write(nd->path.mnt); 2764 if (!error) 2765 got_write = true; 2766 /* 2767 * do _not_ fail yet - we might not need that or fail with 2768 * a different error; let lookup_open() decide; we'll be 2769 * dropping this one anyway. 2770 */ 2771 } 2772 mutex_lock(&dir->d_inode->i_mutex); 2773 error = lookup_open(nd, path, file, op, got_write, opened); 2774 mutex_unlock(&dir->d_inode->i_mutex); 2775 2776 if (error <= 0) { 2777 if (error) 2778 goto out; 2779 2780 if ((*opened & FILE_CREATED) || 2781 !S_ISREG(file->f_path.dentry->d_inode->i_mode)) 2782 will_truncate = false; 2783 2784 audit_inode(name, file->f_path.dentry, 0); 2785 goto opened; 2786 } 2787 2788 if (*opened & FILE_CREATED) { 2789 /* Don't check for write permission, don't truncate */ 2790 open_flag &= ~O_TRUNC; 2791 will_truncate = false; 2792 acc_mode = MAY_OPEN; 2793 path_to_nameidata(path, nd); 2794 goto finish_open_created; 2795 } 2796 2797 /* 2798 * create/update audit record if it already exists. 2799 */ 2800 if (path->dentry->d_inode) 2801 audit_inode(name, path->dentry, 0); 2802 2803 /* 2804 * If atomic_open() acquired write access it is dropped now due to 2805 * possible mount and symlink following (this might be optimized away if 2806 * necessary...) 2807 */ 2808 if (got_write) { 2809 mnt_drop_write(nd->path.mnt); 2810 got_write = false; 2811 } 2812 2813 error = -EEXIST; 2814 if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT)) 2815 goto exit_dput; 2816 2817 error = follow_managed(path, nd->flags); 2818 if (error < 0) 2819 goto exit_dput; 2820 2821 if (error) 2822 nd->flags |= LOOKUP_JUMPED; 2823 2824 BUG_ON(nd->flags & LOOKUP_RCU); 2825 inode = path->dentry->d_inode; 2826 finish_lookup: 2827 /* we _can_ be in RCU mode here */ 2828 error = -ENOENT; 2829 if (!inode) { 2830 path_to_nameidata(path, nd); 2831 goto out; 2832 } 2833 2834 if (should_follow_link(inode, !symlink_ok)) { 2835 if (nd->flags & LOOKUP_RCU) { 2836 if (unlikely(unlazy_walk(nd, path->dentry))) { 2837 error = -ECHILD; 2838 goto out; 2839 } 2840 } 2841 BUG_ON(inode != path->dentry->d_inode); 2842 return 1; 2843 } 2844 2845 if ((nd->flags & LOOKUP_RCU) || nd->path.mnt != path->mnt) { 2846 path_to_nameidata(path, nd); 2847 } else { 2848 save_parent.dentry = nd->path.dentry; 2849 save_parent.mnt = mntget(path->mnt); 2850 nd->path.dentry = path->dentry; 2851 2852 } 2853 nd->inode = inode; 2854 /* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */ 2855 error = complete_walk(nd); 2856 if (error) { 2857 path_put(&save_parent); 2858 return error; 2859 } 2860 error = -EISDIR; 2861 if ((open_flag & O_CREAT) && S_ISDIR(nd->inode->i_mode)) 2862 goto out; 2863 error = -ENOTDIR; 2864 if ((nd->flags & LOOKUP_DIRECTORY) && !nd->inode->i_op->lookup) 2865 goto out; 2866 audit_inode(name, nd->path.dentry, 0); 2867 finish_open: 2868 if (!S_ISREG(nd->inode->i_mode)) 2869 will_truncate = false; 2870 2871 if (will_truncate) { 2872 error = mnt_want_write(nd->path.mnt); 2873 if (error) 2874 goto out; 2875 got_write = true; 2876 } 2877 finish_open_created: 2878 error = may_open(&nd->path, acc_mode, open_flag); 2879 if (error) 2880 goto out; 2881 file->f_path.mnt = nd->path.mnt; 2882 error = finish_open(file, nd->path.dentry, NULL, opened); 2883 if (error) { 2884 if (error == -EOPENSTALE) 2885 goto stale_open; 2886 goto out; 2887 } 2888 opened: 2889 error = open_check_o_direct(file); 2890 if (error) 2891 goto exit_fput; 2892 error = ima_file_check(file, op->acc_mode); 2893 if (error) 2894 goto exit_fput; 2895 2896 if (will_truncate) { 2897 error = handle_truncate(file); 2898 if (error) 2899 goto exit_fput; 2900 } 2901 out: 2902 if (got_write) 2903 mnt_drop_write(nd->path.mnt); 2904 path_put(&save_parent); 2905 terminate_walk(nd); 2906 return error; 2907 2908 exit_dput: 2909 path_put_conditional(path, nd); 2910 goto out; 2911 exit_fput: 2912 fput(file); 2913 goto out; 2914 2915 stale_open: 2916 /* If no saved parent or already retried then can't retry */ 2917 if (!save_parent.dentry || retried) 2918 goto out; 2919 2920 BUG_ON(save_parent.dentry != dir); 2921 path_put(&nd->path); 2922 nd->path = save_parent; 2923 nd->inode = dir->d_inode; 2924 save_parent.mnt = NULL; 2925 save_parent.dentry = NULL; 2926 if (got_write) { 2927 mnt_drop_write(nd->path.mnt); 2928 got_write = false; 2929 } 2930 retried = true; 2931 goto retry_lookup; 2932 } 2933 2934 static struct file *path_openat(int dfd, struct filename *pathname, 2935 struct nameidata *nd, const struct open_flags *op, int flags) 2936 { 2937 struct file *base = NULL; 2938 struct file *file; 2939 struct path path; 2940 int opened = 0; 2941 int error; 2942 2943 file = get_empty_filp(); 2944 if (!file) 2945 return ERR_PTR(-ENFILE); 2946 2947 file->f_flags = op->open_flag; 2948 2949 error = path_init(dfd, pathname->name, flags | LOOKUP_PARENT, nd, &base); 2950 if (unlikely(error)) 2951 goto out; 2952 2953 current->total_link_count = 0; 2954 error = link_path_walk(pathname->name, nd); 2955 if (unlikely(error)) 2956 goto out; 2957 2958 error = do_last(nd, &path, file, op, &opened, pathname); 2959 while (unlikely(error > 0)) { /* trailing symlink */ 2960 struct path link = path; 2961 void *cookie; 2962 if (!(nd->flags & LOOKUP_FOLLOW)) { 2963 path_put_conditional(&path, nd); 2964 path_put(&nd->path); 2965 error = -ELOOP; 2966 break; 2967 } 2968 error = may_follow_link(&link, nd); 2969 if (unlikely(error)) 2970 break; 2971 nd->flags |= LOOKUP_PARENT; 2972 nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL); 2973 error = follow_link(&link, nd, &cookie); 2974 if (unlikely(error)) 2975 break; 2976 error = do_last(nd, &path, file, op, &opened, pathname); 2977 put_link(nd, &link, cookie); 2978 } 2979 out: 2980 if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) 2981 path_put(&nd->root); 2982 if (base) 2983 fput(base); 2984 if (!(opened & FILE_OPENED)) { 2985 BUG_ON(!error); 2986 put_filp(file); 2987 } 2988 if (unlikely(error)) { 2989 if (error == -EOPENSTALE) { 2990 if (flags & LOOKUP_RCU) 2991 error = -ECHILD; 2992 else 2993 error = -ESTALE; 2994 } 2995 file = ERR_PTR(error); 2996 } 2997 return file; 2998 } 2999 3000 struct file *do_filp_open(int dfd, struct filename *pathname, 3001 const struct open_flags *op, int flags) 3002 { 3003 struct nameidata nd; 3004 struct file *filp; 3005 3006 filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU); 3007 if (unlikely(filp == ERR_PTR(-ECHILD))) 3008 filp = path_openat(dfd, pathname, &nd, op, flags); 3009 if (unlikely(filp == ERR_PTR(-ESTALE))) 3010 filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL); 3011 return filp; 3012 } 3013 3014 struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, 3015 const char *name, const struct open_flags *op, int flags) 3016 { 3017 struct nameidata nd; 3018 struct file *file; 3019 struct filename filename = { .name = name }; 3020 3021 nd.root.mnt = mnt; 3022 nd.root.dentry = dentry; 3023 3024 flags |= LOOKUP_ROOT; 3025 3026 if (dentry->d_inode->i_op->follow_link && op->intent & LOOKUP_OPEN) 3027 return ERR_PTR(-ELOOP); 3028 3029 file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_RCU); 3030 if (unlikely(file == ERR_PTR(-ECHILD))) 3031 file = path_openat(-1, &filename, &nd, op, flags); 3032 if (unlikely(file == ERR_PTR(-ESTALE))) 3033 file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_REVAL); 3034 return file; 3035 } 3036 3037 struct dentry *kern_path_create(int dfd, const char *pathname, 3038 struct path *path, unsigned int lookup_flags) 3039 { 3040 struct dentry *dentry = ERR_PTR(-EEXIST); 3041 struct nameidata nd; 3042 int err2; 3043 int error; 3044 bool is_dir = (lookup_flags & LOOKUP_DIRECTORY); 3045 3046 /* 3047 * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any 3048 * other flags passed in are ignored! 3049 */ 3050 lookup_flags &= LOOKUP_REVAL; 3051 3052 error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd); 3053 if (error) 3054 return ERR_PTR(error); 3055 3056 /* 3057 * Yucky last component or no last component at all? 3058 * (foo/., foo/.., /////) 3059 */ 3060 if (nd.last_type != LAST_NORM) 3061 goto out; 3062 nd.flags &= ~LOOKUP_PARENT; 3063 nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL; 3064 3065 /* don't fail immediately if it's r/o, at least try to report other errors */ 3066 err2 = mnt_want_write(nd.path.mnt); 3067 /* 3068 * Do the final lookup. 3069 */ 3070 mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); 3071 dentry = lookup_hash(&nd); 3072 if (IS_ERR(dentry)) 3073 goto unlock; 3074 3075 error = -EEXIST; 3076 if (dentry->d_inode) 3077 goto fail; 3078 /* 3079 * Special case - lookup gave negative, but... we had foo/bar/ 3080 * From the vfs_mknod() POV we just have a negative dentry - 3081 * all is fine. Let's be bastards - you had / on the end, you've 3082 * been asking for (non-existent) directory. -ENOENT for you. 3083 */ 3084 if (unlikely(!is_dir && nd.last.name[nd.last.len])) { 3085 error = -ENOENT; 3086 goto fail; 3087 } 3088 if (unlikely(err2)) { 3089 error = err2; 3090 goto fail; 3091 } 3092 *path = nd.path; 3093 return dentry; 3094 fail: 3095 dput(dentry); 3096 dentry = ERR_PTR(error); 3097 unlock: 3098 mutex_unlock(&nd.path.dentry->d_inode->i_mutex); 3099 if (!err2) 3100 mnt_drop_write(nd.path.mnt); 3101 out: 3102 path_put(&nd.path); 3103 return dentry; 3104 } 3105 EXPORT_SYMBOL(kern_path_create); 3106 3107 void done_path_create(struct path *path, struct dentry *dentry) 3108 { 3109 dput(dentry); 3110 mutex_unlock(&path->dentry->d_inode->i_mutex); 3111 mnt_drop_write(path->mnt); 3112 path_put(path); 3113 } 3114 EXPORT_SYMBOL(done_path_create); 3115 3116 struct dentry *user_path_create(int dfd, const char __user *pathname, 3117 struct path *path, unsigned int lookup_flags) 3118 { 3119 struct filename *tmp = getname(pathname); 3120 struct dentry *res; 3121 if (IS_ERR(tmp)) 3122 return ERR_CAST(tmp); 3123 res = kern_path_create(dfd, tmp->name, path, lookup_flags); 3124 putname(tmp); 3125 return res; 3126 } 3127 EXPORT_SYMBOL(user_path_create); 3128 3129 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev) 3130 { 3131 int error = may_create(dir, dentry); 3132 3133 if (error) 3134 return error; 3135 3136 if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD)) 3137 return -EPERM; 3138 3139 if (!dir->i_op->mknod) 3140 return -EPERM; 3141 3142 error = devcgroup_inode_mknod(mode, dev); 3143 if (error) 3144 return error; 3145 3146 error = security_inode_mknod(dir, dentry, mode, dev); 3147 if (error) 3148 return error; 3149 3150 error = dir->i_op->mknod(dir, dentry, mode, dev); 3151 if (!error) 3152 fsnotify_create(dir, dentry); 3153 return error; 3154 } 3155 3156 static int may_mknod(umode_t mode) 3157 { 3158 switch (mode & S_IFMT) { 3159 case S_IFREG: 3160 case S_IFCHR: 3161 case S_IFBLK: 3162 case S_IFIFO: 3163 case S_IFSOCK: 3164 case 0: /* zero mode translates to S_IFREG */ 3165 return 0; 3166 case S_IFDIR: 3167 return -EPERM; 3168 default: 3169 return -EINVAL; 3170 } 3171 } 3172 3173 SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode, 3174 unsigned, dev) 3175 { 3176 struct dentry *dentry; 3177 struct path path; 3178 int error; 3179 unsigned int lookup_flags = 0; 3180 3181 error = may_mknod(mode); 3182 if (error) 3183 return error; 3184 retry: 3185 dentry = user_path_create(dfd, filename, &path, lookup_flags); 3186 if (IS_ERR(dentry)) 3187 return PTR_ERR(dentry); 3188 3189 if (!IS_POSIXACL(path.dentry->d_inode)) 3190 mode &= ~current_umask(); 3191 error = security_path_mknod(&path, dentry, mode, dev); 3192 if (error) 3193 goto out; 3194 switch (mode & S_IFMT) { 3195 case 0: case S_IFREG: 3196 error = vfs_create(path.dentry->d_inode,dentry,mode,true); 3197 break; 3198 case S_IFCHR: case S_IFBLK: 3199 error = vfs_mknod(path.dentry->d_inode,dentry,mode, 3200 new_decode_dev(dev)); 3201 break; 3202 case S_IFIFO: case S_IFSOCK: 3203 error = vfs_mknod(path.dentry->d_inode,dentry,mode,0); 3204 break; 3205 } 3206 out: 3207 done_path_create(&path, dentry); 3208 if (retry_estale(error, lookup_flags)) { 3209 lookup_flags |= LOOKUP_REVAL; 3210 goto retry; 3211 } 3212 return error; 3213 } 3214 3215 SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev) 3216 { 3217 return sys_mknodat(AT_FDCWD, filename, mode, dev); 3218 } 3219 3220 int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode) 3221 { 3222 int error = may_create(dir, dentry); 3223 unsigned max_links = dir->i_sb->s_max_links; 3224 3225 if (error) 3226 return error; 3227 3228 if (!dir->i_op->mkdir) 3229 return -EPERM; 3230 3231 mode &= (S_IRWXUGO|S_ISVTX); 3232 error = security_inode_mkdir(dir, dentry, mode); 3233 if (error) 3234 return error; 3235 3236 if (max_links && dir->i_nlink >= max_links) 3237 return -EMLINK; 3238 3239 error = dir->i_op->mkdir(dir, dentry, mode); 3240 if (!error) 3241 fsnotify_mkdir(dir, dentry); 3242 return error; 3243 } 3244 3245 SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode) 3246 { 3247 struct dentry *dentry; 3248 struct path path; 3249 int error; 3250 unsigned int lookup_flags = LOOKUP_DIRECTORY; 3251 3252 retry: 3253 dentry = user_path_create(dfd, pathname, &path, lookup_flags); 3254 if (IS_ERR(dentry)) 3255 return PTR_ERR(dentry); 3256 3257 if (!IS_POSIXACL(path.dentry->d_inode)) 3258 mode &= ~current_umask(); 3259 error = security_path_mkdir(&path, dentry, mode); 3260 if (!error) 3261 error = vfs_mkdir(path.dentry->d_inode, dentry, mode); 3262 done_path_create(&path, dentry); 3263 if (retry_estale(error, lookup_flags)) { 3264 lookup_flags |= LOOKUP_REVAL; 3265 goto retry; 3266 } 3267 return error; 3268 } 3269 3270 SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode) 3271 { 3272 return sys_mkdirat(AT_FDCWD, pathname, mode); 3273 } 3274 3275 /* 3276 * The dentry_unhash() helper will try to drop the dentry early: we 3277 * should have a usage count of 1 if we're the only user of this 3278 * dentry, and if that is true (possibly after pruning the dcache), 3279 * then we drop the dentry now. 3280 * 3281 * A low-level filesystem can, if it choses, legally 3282 * do a 3283 * 3284 * if (!d_unhashed(dentry)) 3285 * return -EBUSY; 3286 * 3287 * if it cannot handle the case of removing a directory 3288 * that is still in use by something else.. 3289 */ 3290 void dentry_unhash(struct dentry *dentry) 3291 { 3292 shrink_dcache_parent(dentry); 3293 spin_lock(&dentry->d_lock); 3294 if (dentry->d_count == 1) 3295 __d_drop(dentry); 3296 spin_unlock(&dentry->d_lock); 3297 } 3298 3299 int vfs_rmdir(struct inode *dir, struct dentry *dentry) 3300 { 3301 int error = may_delete(dir, dentry, 1); 3302 3303 if (error) 3304 return error; 3305 3306 if (!dir->i_op->rmdir) 3307 return -EPERM; 3308 3309 dget(dentry); 3310 mutex_lock(&dentry->d_inode->i_mutex); 3311 3312 error = -EBUSY; 3313 if (d_mountpoint(dentry)) 3314 goto out; 3315 3316 error = security_inode_rmdir(dir, dentry); 3317 if (error) 3318 goto out; 3319 3320 shrink_dcache_parent(dentry); 3321 error = dir->i_op->rmdir(dir, dentry); 3322 if (error) 3323 goto out; 3324 3325 dentry->d_inode->i_flags |= S_DEAD; 3326 dont_mount(dentry); 3327 3328 out: 3329 mutex_unlock(&dentry->d_inode->i_mutex); 3330 dput(dentry); 3331 if (!error) 3332 d_delete(dentry); 3333 return error; 3334 } 3335 3336 static long do_rmdir(int dfd, const char __user *pathname) 3337 { 3338 int error = 0; 3339 struct filename *name; 3340 struct dentry *dentry; 3341 struct nameidata nd; 3342 unsigned int lookup_flags = 0; 3343 retry: 3344 name = user_path_parent(dfd, pathname, &nd, lookup_flags); 3345 if (IS_ERR(name)) 3346 return PTR_ERR(name); 3347 3348 switch(nd.last_type) { 3349 case LAST_DOTDOT: 3350 error = -ENOTEMPTY; 3351 goto exit1; 3352 case LAST_DOT: 3353 error = -EINVAL; 3354 goto exit1; 3355 case LAST_ROOT: 3356 error = -EBUSY; 3357 goto exit1; 3358 } 3359 3360 nd.flags &= ~LOOKUP_PARENT; 3361 error = mnt_want_write(nd.path.mnt); 3362 if (error) 3363 goto exit1; 3364 3365 mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); 3366 dentry = lookup_hash(&nd); 3367 error = PTR_ERR(dentry); 3368 if (IS_ERR(dentry)) 3369 goto exit2; 3370 if (!dentry->d_inode) { 3371 error = -ENOENT; 3372 goto exit3; 3373 } 3374 error = security_path_rmdir(&nd.path, dentry); 3375 if (error) 3376 goto exit3; 3377 error = vfs_rmdir(nd.path.dentry->d_inode, dentry); 3378 exit3: 3379 dput(dentry); 3380 exit2: 3381 mutex_unlock(&nd.path.dentry->d_inode->i_mutex); 3382 mnt_drop_write(nd.path.mnt); 3383 exit1: 3384 path_put(&nd.path); 3385 putname(name); 3386 if (retry_estale(error, lookup_flags)) { 3387 lookup_flags |= LOOKUP_REVAL; 3388 goto retry; 3389 } 3390 return error; 3391 } 3392 3393 SYSCALL_DEFINE1(rmdir, const char __user *, pathname) 3394 { 3395 return do_rmdir(AT_FDCWD, pathname); 3396 } 3397 3398 int vfs_unlink(struct inode *dir, struct dentry *dentry) 3399 { 3400 int error = may_delete(dir, dentry, 0); 3401 3402 if (error) 3403 return error; 3404 3405 if (!dir->i_op->unlink) 3406 return -EPERM; 3407 3408 mutex_lock(&dentry->d_inode->i_mutex); 3409 if (d_mountpoint(dentry)) 3410 error = -EBUSY; 3411 else { 3412 error = security_inode_unlink(dir, dentry); 3413 if (!error) { 3414 error = dir->i_op->unlink(dir, dentry); 3415 if (!error) 3416 dont_mount(dentry); 3417 } 3418 } 3419 mutex_unlock(&dentry->d_inode->i_mutex); 3420 3421 /* We don't d_delete() NFS sillyrenamed files--they still exist. */ 3422 if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) { 3423 fsnotify_link_count(dentry->d_inode); 3424 d_delete(dentry); 3425 } 3426 3427 return error; 3428 } 3429 3430 /* 3431 * Make sure that the actual truncation of the file will occur outside its 3432 * directory's i_mutex. Truncate can take a long time if there is a lot of 3433 * writeout happening, and we don't want to prevent access to the directory 3434 * while waiting on the I/O. 3435 */ 3436 static long do_unlinkat(int dfd, const char __user *pathname) 3437 { 3438 int error; 3439 struct filename *name; 3440 struct dentry *dentry; 3441 struct nameidata nd; 3442 struct inode *inode = NULL; 3443 unsigned int lookup_flags = 0; 3444 retry: 3445 name = user_path_parent(dfd, pathname, &nd, lookup_flags); 3446 if (IS_ERR(name)) 3447 return PTR_ERR(name); 3448 3449 error = -EISDIR; 3450 if (nd.last_type != LAST_NORM) 3451 goto exit1; 3452 3453 nd.flags &= ~LOOKUP_PARENT; 3454 error = mnt_want_write(nd.path.mnt); 3455 if (error) 3456 goto exit1; 3457 3458 mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); 3459 dentry = lookup_hash(&nd); 3460 error = PTR_ERR(dentry); 3461 if (!IS_ERR(dentry)) { 3462 /* Why not before? Because we want correct error value */ 3463 if (nd.last.name[nd.last.len]) 3464 goto slashes; 3465 inode = dentry->d_inode; 3466 if (!inode) 3467 goto slashes; 3468 ihold(inode); 3469 error = security_path_unlink(&nd.path, dentry); 3470 if (error) 3471 goto exit2; 3472 error = vfs_unlink(nd.path.dentry->d_inode, dentry); 3473 exit2: 3474 dput(dentry); 3475 } 3476 mutex_unlock(&nd.path.dentry->d_inode->i_mutex); 3477 if (inode) 3478 iput(inode); /* truncate the inode here */ 3479 mnt_drop_write(nd.path.mnt); 3480 exit1: 3481 path_put(&nd.path); 3482 putname(name); 3483 if (retry_estale(error, lookup_flags)) { 3484 lookup_flags |= LOOKUP_REVAL; 3485 inode = NULL; 3486 goto retry; 3487 } 3488 return error; 3489 3490 slashes: 3491 error = !dentry->d_inode ? -ENOENT : 3492 S_ISDIR(dentry->d_inode->i_mode) ? -EISDIR : -ENOTDIR; 3493 goto exit2; 3494 } 3495 3496 SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag) 3497 { 3498 if ((flag & ~AT_REMOVEDIR) != 0) 3499 return -EINVAL; 3500 3501 if (flag & AT_REMOVEDIR) 3502 return do_rmdir(dfd, pathname); 3503 3504 return do_unlinkat(dfd, pathname); 3505 } 3506 3507 SYSCALL_DEFINE1(unlink, const char __user *, pathname) 3508 { 3509 return do_unlinkat(AT_FDCWD, pathname); 3510 } 3511 3512 int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname) 3513 { 3514 int error = may_create(dir, dentry); 3515 3516 if (error) 3517 return error; 3518 3519 if (!dir->i_op->symlink) 3520 return -EPERM; 3521 3522 error = security_inode_symlink(dir, dentry, oldname); 3523 if (error) 3524 return error; 3525 3526 error = dir->i_op->symlink(dir, dentry, oldname); 3527 if (!error) 3528 fsnotify_create(dir, dentry); 3529 return error; 3530 } 3531 3532 SYSCALL_DEFINE3(symlinkat, const char __user *, oldname, 3533 int, newdfd, const char __user *, newname) 3534 { 3535 int error; 3536 struct filename *from; 3537 struct dentry *dentry; 3538 struct path path; 3539 unsigned int lookup_flags = 0; 3540 3541 from = getname(oldname); 3542 if (IS_ERR(from)) 3543 return PTR_ERR(from); 3544 retry: 3545 dentry = user_path_create(newdfd, newname, &path, lookup_flags); 3546 error = PTR_ERR(dentry); 3547 if (IS_ERR(dentry)) 3548 goto out_putname; 3549 3550 error = security_path_symlink(&path, dentry, from->name); 3551 if (!error) 3552 error = vfs_symlink(path.dentry->d_inode, dentry, from->name); 3553 done_path_create(&path, dentry); 3554 if (retry_estale(error, lookup_flags)) { 3555 lookup_flags |= LOOKUP_REVAL; 3556 goto retry; 3557 } 3558 out_putname: 3559 putname(from); 3560 return error; 3561 } 3562 3563 SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname) 3564 { 3565 return sys_symlinkat(oldname, AT_FDCWD, newname); 3566 } 3567 3568 int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry) 3569 { 3570 struct inode *inode = old_dentry->d_inode; 3571 unsigned max_links = dir->i_sb->s_max_links; 3572 int error; 3573 3574 if (!inode) 3575 return -ENOENT; 3576 3577 error = may_create(dir, new_dentry); 3578 if (error) 3579 return error; 3580 3581 if (dir->i_sb != inode->i_sb) 3582 return -EXDEV; 3583 3584 /* 3585 * A link to an append-only or immutable file cannot be created. 3586 */ 3587 if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) 3588 return -EPERM; 3589 if (!dir->i_op->link) 3590 return -EPERM; 3591 if (S_ISDIR(inode->i_mode)) 3592 return -EPERM; 3593 3594 error = security_inode_link(old_dentry, dir, new_dentry); 3595 if (error) 3596 return error; 3597 3598 mutex_lock(&inode->i_mutex); 3599 /* Make sure we don't allow creating hardlink to an unlinked file */ 3600 if (inode->i_nlink == 0) 3601 error = -ENOENT; 3602 else if (max_links && inode->i_nlink >= max_links) 3603 error = -EMLINK; 3604 else 3605 error = dir->i_op->link(old_dentry, dir, new_dentry); 3606 mutex_unlock(&inode->i_mutex); 3607 if (!error) 3608 fsnotify_link(dir, inode, new_dentry); 3609 return error; 3610 } 3611 3612 /* 3613 * Hardlinks are often used in delicate situations. We avoid 3614 * security-related surprises by not following symlinks on the 3615 * newname. --KAB 3616 * 3617 * We don't follow them on the oldname either to be compatible 3618 * with linux 2.0, and to avoid hard-linking to directories 3619 * and other special files. --ADM 3620 */ 3621 SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname, 3622 int, newdfd, const char __user *, newname, int, flags) 3623 { 3624 struct dentry *new_dentry; 3625 struct path old_path, new_path; 3626 int how = 0; 3627 int error; 3628 3629 if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) 3630 return -EINVAL; 3631 /* 3632 * To use null names we require CAP_DAC_READ_SEARCH 3633 * This ensures that not everyone will be able to create 3634 * handlink using the passed filedescriptor. 3635 */ 3636 if (flags & AT_EMPTY_PATH) { 3637 if (!capable(CAP_DAC_READ_SEARCH)) 3638 return -ENOENT; 3639 how = LOOKUP_EMPTY; 3640 } 3641 3642 if (flags & AT_SYMLINK_FOLLOW) 3643 how |= LOOKUP_FOLLOW; 3644 retry: 3645 error = user_path_at(olddfd, oldname, how, &old_path); 3646 if (error) 3647 return error; 3648 3649 new_dentry = user_path_create(newdfd, newname, &new_path, 3650 (how & LOOKUP_REVAL)); 3651 error = PTR_ERR(new_dentry); 3652 if (IS_ERR(new_dentry)) 3653 goto out; 3654 3655 error = -EXDEV; 3656 if (old_path.mnt != new_path.mnt) 3657 goto out_dput; 3658 error = may_linkat(&old_path); 3659 if (unlikely(error)) 3660 goto out_dput; 3661 error = security_path_link(old_path.dentry, &new_path, new_dentry); 3662 if (error) 3663 goto out_dput; 3664 error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry); 3665 out_dput: 3666 done_path_create(&new_path, new_dentry); 3667 if (retry_estale(error, how)) { 3668 how |= LOOKUP_REVAL; 3669 goto retry; 3670 } 3671 out: 3672 path_put(&old_path); 3673 3674 return error; 3675 } 3676 3677 SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname) 3678 { 3679 return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0); 3680 } 3681 3682 /* 3683 * The worst of all namespace operations - renaming directory. "Perverted" 3684 * doesn't even start to describe it. Somebody in UCB had a heck of a trip... 3685 * Problems: 3686 * a) we can get into loop creation. Check is done in is_subdir(). 3687 * b) race potential - two innocent renames can create a loop together. 3688 * That's where 4.4 screws up. Current fix: serialization on 3689 * sb->s_vfs_rename_mutex. We might be more accurate, but that's another 3690 * story. 3691 * c) we have to lock _three_ objects - parents and victim (if it exists). 3692 * And that - after we got ->i_mutex on parents (until then we don't know 3693 * whether the target exists). Solution: try to be smart with locking 3694 * order for inodes. We rely on the fact that tree topology may change 3695 * only under ->s_vfs_rename_mutex _and_ that parent of the object we 3696 * move will be locked. Thus we can rank directories by the tree 3697 * (ancestors first) and rank all non-directories after them. 3698 * That works since everybody except rename does "lock parent, lookup, 3699 * lock child" and rename is under ->s_vfs_rename_mutex. 3700 * HOWEVER, it relies on the assumption that any object with ->lookup() 3701 * has no more than 1 dentry. If "hybrid" objects will ever appear, 3702 * we'd better make sure that there's no link(2) for them. 3703 * d) conversion from fhandle to dentry may come in the wrong moment - when 3704 * we are removing the target. Solution: we will have to grab ->i_mutex 3705 * in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on 3706 * ->i_mutex on parents, which works but leads to some truly excessive 3707 * locking]. 3708 */ 3709 static int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry, 3710 struct inode *new_dir, struct dentry *new_dentry) 3711 { 3712 int error = 0; 3713 struct inode *target = new_dentry->d_inode; 3714 unsigned max_links = new_dir->i_sb->s_max_links; 3715 3716 /* 3717 * If we are going to change the parent - check write permissions, 3718 * we'll need to flip '..'. 3719 */ 3720 if (new_dir != old_dir) { 3721 error = inode_permission(old_dentry->d_inode, MAY_WRITE); 3722 if (error) 3723 return error; 3724 } 3725 3726 error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry); 3727 if (error) 3728 return error; 3729 3730 dget(new_dentry); 3731 if (target) 3732 mutex_lock(&target->i_mutex); 3733 3734 error = -EBUSY; 3735 if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry)) 3736 goto out; 3737 3738 error = -EMLINK; 3739 if (max_links && !target && new_dir != old_dir && 3740 new_dir->i_nlink >= max_links) 3741 goto out; 3742 3743 if (target) 3744 shrink_dcache_parent(new_dentry); 3745 error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry); 3746 if (error) 3747 goto out; 3748 3749 if (target) { 3750 target->i_flags |= S_DEAD; 3751 dont_mount(new_dentry); 3752 } 3753 out: 3754 if (target) 3755 mutex_unlock(&target->i_mutex); 3756 dput(new_dentry); 3757 if (!error) 3758 if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) 3759 d_move(old_dentry,new_dentry); 3760 return error; 3761 } 3762 3763 static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry, 3764 struct inode *new_dir, struct dentry *new_dentry) 3765 { 3766 struct inode *target = new_dentry->d_inode; 3767 int error; 3768 3769 error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry); 3770 if (error) 3771 return error; 3772 3773 dget(new_dentry); 3774 if (target) 3775 mutex_lock(&target->i_mutex); 3776 3777 error = -EBUSY; 3778 if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry)) 3779 goto out; 3780 3781 error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry); 3782 if (error) 3783 goto out; 3784 3785 if (target) 3786 dont_mount(new_dentry); 3787 if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) 3788 d_move(old_dentry, new_dentry); 3789 out: 3790 if (target) 3791 mutex_unlock(&target->i_mutex); 3792 dput(new_dentry); 3793 return error; 3794 } 3795 3796 int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, 3797 struct inode *new_dir, struct dentry *new_dentry) 3798 { 3799 int error; 3800 int is_dir = S_ISDIR(old_dentry->d_inode->i_mode); 3801 const unsigned char *old_name; 3802 3803 if (old_dentry->d_inode == new_dentry->d_inode) 3804 return 0; 3805 3806 error = may_delete(old_dir, old_dentry, is_dir); 3807 if (error) 3808 return error; 3809 3810 if (!new_dentry->d_inode) 3811 error = may_create(new_dir, new_dentry); 3812 else 3813 error = may_delete(new_dir, new_dentry, is_dir); 3814 if (error) 3815 return error; 3816 3817 if (!old_dir->i_op->rename) 3818 return -EPERM; 3819 3820 old_name = fsnotify_oldname_init(old_dentry->d_name.name); 3821 3822 if (is_dir) 3823 error = vfs_rename_dir(old_dir,old_dentry,new_dir,new_dentry); 3824 else 3825 error = vfs_rename_other(old_dir,old_dentry,new_dir,new_dentry); 3826 if (!error) 3827 fsnotify_move(old_dir, new_dir, old_name, is_dir, 3828 new_dentry->d_inode, old_dentry); 3829 fsnotify_oldname_free(old_name); 3830 3831 return error; 3832 } 3833 3834 SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname, 3835 int, newdfd, const char __user *, newname) 3836 { 3837 struct dentry *old_dir, *new_dir; 3838 struct dentry *old_dentry, *new_dentry; 3839 struct dentry *trap; 3840 struct nameidata oldnd, newnd; 3841 struct filename *from; 3842 struct filename *to; 3843 unsigned int lookup_flags = 0; 3844 bool should_retry = false; 3845 int error; 3846 retry: 3847 from = user_path_parent(olddfd, oldname, &oldnd, lookup_flags); 3848 if (IS_ERR(from)) { 3849 error = PTR_ERR(from); 3850 goto exit; 3851 } 3852 3853 to = user_path_parent(newdfd, newname, &newnd, lookup_flags); 3854 if (IS_ERR(to)) { 3855 error = PTR_ERR(to); 3856 goto exit1; 3857 } 3858 3859 error = -EXDEV; 3860 if (oldnd.path.mnt != newnd.path.mnt) 3861 goto exit2; 3862 3863 old_dir = oldnd.path.dentry; 3864 error = -EBUSY; 3865 if (oldnd.last_type != LAST_NORM) 3866 goto exit2; 3867 3868 new_dir = newnd.path.dentry; 3869 if (newnd.last_type != LAST_NORM) 3870 goto exit2; 3871 3872 error = mnt_want_write(oldnd.path.mnt); 3873 if (error) 3874 goto exit2; 3875 3876 oldnd.flags &= ~LOOKUP_PARENT; 3877 newnd.flags &= ~LOOKUP_PARENT; 3878 newnd.flags |= LOOKUP_RENAME_TARGET; 3879 3880 trap = lock_rename(new_dir, old_dir); 3881 3882 old_dentry = lookup_hash(&oldnd); 3883 error = PTR_ERR(old_dentry); 3884 if (IS_ERR(old_dentry)) 3885 goto exit3; 3886 /* source must exist */ 3887 error = -ENOENT; 3888 if (!old_dentry->d_inode) 3889 goto exit4; 3890 /* unless the source is a directory trailing slashes give -ENOTDIR */ 3891 if (!S_ISDIR(old_dentry->d_inode->i_mode)) { 3892 error = -ENOTDIR; 3893 if (oldnd.last.name[oldnd.last.len]) 3894 goto exit4; 3895 if (newnd.last.name[newnd.last.len]) 3896 goto exit4; 3897 } 3898 /* source should not be ancestor of target */ 3899 error = -EINVAL; 3900 if (old_dentry == trap) 3901 goto exit4; 3902 new_dentry = lookup_hash(&newnd); 3903 error = PTR_ERR(new_dentry); 3904 if (IS_ERR(new_dentry)) 3905 goto exit4; 3906 /* target should not be an ancestor of source */ 3907 error = -ENOTEMPTY; 3908 if (new_dentry == trap) 3909 goto exit5; 3910 3911 error = security_path_rename(&oldnd.path, old_dentry, 3912 &newnd.path, new_dentry); 3913 if (error) 3914 goto exit5; 3915 error = vfs_rename(old_dir->d_inode, old_dentry, 3916 new_dir->d_inode, new_dentry); 3917 exit5: 3918 dput(new_dentry); 3919 exit4: 3920 dput(old_dentry); 3921 exit3: 3922 unlock_rename(new_dir, old_dir); 3923 mnt_drop_write(oldnd.path.mnt); 3924 exit2: 3925 if (retry_estale(error, lookup_flags)) 3926 should_retry = true; 3927 path_put(&newnd.path); 3928 putname(to); 3929 exit1: 3930 path_put(&oldnd.path); 3931 putname(from); 3932 if (should_retry) { 3933 should_retry = false; 3934 lookup_flags |= LOOKUP_REVAL; 3935 goto retry; 3936 } 3937 exit: 3938 return error; 3939 } 3940 3941 SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname) 3942 { 3943 return sys_renameat(AT_FDCWD, oldname, AT_FDCWD, newname); 3944 } 3945 3946 int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen, const char *link) 3947 { 3948 int len; 3949 3950 len = PTR_ERR(link); 3951 if (IS_ERR(link)) 3952 goto out; 3953 3954 len = strlen(link); 3955 if (len > (unsigned) buflen) 3956 len = buflen; 3957 if (copy_to_user(buffer, link, len)) 3958 len = -EFAULT; 3959 out: 3960 return len; 3961 } 3962 3963 /* 3964 * A helper for ->readlink(). This should be used *ONLY* for symlinks that 3965 * have ->follow_link() touching nd only in nd_set_link(). Using (or not 3966 * using) it for any given inode is up to filesystem. 3967 */ 3968 int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen) 3969 { 3970 struct nameidata nd; 3971 void *cookie; 3972 int res; 3973 3974 nd.depth = 0; 3975 cookie = dentry->d_inode->i_op->follow_link(dentry, &nd); 3976 if (IS_ERR(cookie)) 3977 return PTR_ERR(cookie); 3978 3979 res = vfs_readlink(dentry, buffer, buflen, nd_get_link(&nd)); 3980 if (dentry->d_inode->i_op->put_link) 3981 dentry->d_inode->i_op->put_link(dentry, &nd, cookie); 3982 return res; 3983 } 3984 3985 int vfs_follow_link(struct nameidata *nd, const char *link) 3986 { 3987 return __vfs_follow_link(nd, link); 3988 } 3989 3990 /* get the link contents into pagecache */ 3991 static char *page_getlink(struct dentry * dentry, struct page **ppage) 3992 { 3993 char *kaddr; 3994 struct page *page; 3995 struct address_space *mapping = dentry->d_inode->i_mapping; 3996 page = read_mapping_page(mapping, 0, NULL); 3997 if (IS_ERR(page)) 3998 return (char*)page; 3999 *ppage = page; 4000 kaddr = kmap(page); 4001 nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1); 4002 return kaddr; 4003 } 4004 4005 int page_readlink(struct dentry *dentry, char __user *buffer, int buflen) 4006 { 4007 struct page *page = NULL; 4008 char *s = page_getlink(dentry, &page); 4009 int res = vfs_readlink(dentry,buffer,buflen,s); 4010 if (page) { 4011 kunmap(page); 4012 page_cache_release(page); 4013 } 4014 return res; 4015 } 4016 4017 void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd) 4018 { 4019 struct page *page = NULL; 4020 nd_set_link(nd, page_getlink(dentry, &page)); 4021 return page; 4022 } 4023 4024 void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 4025 { 4026 struct page *page = cookie; 4027 4028 if (page) { 4029 kunmap(page); 4030 page_cache_release(page); 4031 } 4032 } 4033 4034 /* 4035 * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS 4036 */ 4037 int __page_symlink(struct inode *inode, const char *symname, int len, int nofs) 4038 { 4039 struct address_space *mapping = inode->i_mapping; 4040 struct page *page; 4041 void *fsdata; 4042 int err; 4043 char *kaddr; 4044 unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE; 4045 if (nofs) 4046 flags |= AOP_FLAG_NOFS; 4047 4048 retry: 4049 err = pagecache_write_begin(NULL, mapping, 0, len-1, 4050 flags, &page, &fsdata); 4051 if (err) 4052 goto fail; 4053 4054 kaddr = kmap_atomic(page); 4055 memcpy(kaddr, symname, len-1); 4056 kunmap_atomic(kaddr); 4057 4058 err = pagecache_write_end(NULL, mapping, 0, len-1, len-1, 4059 page, fsdata); 4060 if (err < 0) 4061 goto fail; 4062 if (err < len-1) 4063 goto retry; 4064 4065 mark_inode_dirty(inode); 4066 return 0; 4067 fail: 4068 return err; 4069 } 4070 4071 int page_symlink(struct inode *inode, const char *symname, int len) 4072 { 4073 return __page_symlink(inode, symname, len, 4074 !(mapping_gfp_mask(inode->i_mapping) & __GFP_FS)); 4075 } 4076 4077 const struct inode_operations page_symlink_inode_operations = { 4078 .readlink = generic_readlink, 4079 .follow_link = page_follow_link_light, 4080 .put_link = page_put_link, 4081 }; 4082 4083 EXPORT_SYMBOL(user_path_at); 4084 EXPORT_SYMBOL(follow_down_one); 4085 EXPORT_SYMBOL(follow_down); 4086 EXPORT_SYMBOL(follow_up); 4087 EXPORT_SYMBOL(get_write_access); /* nfsd */ 4088 EXPORT_SYMBOL(lock_rename); 4089 EXPORT_SYMBOL(lookup_one_len); 4090 EXPORT_SYMBOL(page_follow_link_light); 4091 EXPORT_SYMBOL(page_put_link); 4092 EXPORT_SYMBOL(page_readlink); 4093 EXPORT_SYMBOL(__page_symlink); 4094 EXPORT_SYMBOL(page_symlink); 4095 EXPORT_SYMBOL(page_symlink_inode_operations); 4096 EXPORT_SYMBOL(kern_path); 4097 EXPORT_SYMBOL(vfs_path_lookup); 4098 EXPORT_SYMBOL(inode_permission); 4099 EXPORT_SYMBOL(unlock_rename); 4100 EXPORT_SYMBOL(vfs_create); 4101 EXPORT_SYMBOL(vfs_follow_link); 4102 EXPORT_SYMBOL(vfs_link); 4103 EXPORT_SYMBOL(vfs_mkdir); 4104 EXPORT_SYMBOL(vfs_mknod); 4105 EXPORT_SYMBOL(generic_permission); 4106 EXPORT_SYMBOL(vfs_readlink); 4107 EXPORT_SYMBOL(vfs_rename); 4108 EXPORT_SYMBOL(vfs_rmdir); 4109 EXPORT_SYMBOL(vfs_symlink); 4110 EXPORT_SYMBOL(vfs_unlink); 4111 EXPORT_SYMBOL(dentry_unhash); 4112 EXPORT_SYMBOL(generic_readlink); 4113